Merge branch 'mon-070-result-no-exceptions' into 'master'

Use Mon's Result<T>

See merge request kemitix/gitdb!1

pom.xml

@@ -21,7 +21,7 @@
         <jgit.version>4.11.0.201803080745-r</jgit.version>
         <junit.version>5.2.0</junit.version>
         <assertj.version>3.10.0</assertj.version>
-        <mon.version>0.4.0</mon.version>
+        <mon.version>0.8.0</mon.version>
         <mockito.version>2.18.3</mockito.version>
         <java-semver.version>0.9.0</java-semver.version>
     </properties>

src/main/java/net/kemitix/gitdb/GitDB.java

@@ -22,10 +22,10 @@
 package net.kemitix.gitdb;
 
 import net.kemitix.gitdb.impl.LocalGitDB;
+import net.kemitix.mon.maybe.Maybe;
+import net.kemitix.mon.result.Result;
 
-import java.io.IOException;
 import java.nio.file.Path;
-import java.util.Optional;
 
 /**
  * Main API for connecting to a Git repo as a database.
@@ -41,13 +41,12 @@ public interface GitDB {
      * @param userName         the user name
      * @param userEmailAddress the user email address
      * @return a GitDB instance for the created local gitdb
-     * @throws IOException if there {@code dbDir} is a file or a non-empty directory
      */
-    static GitDB initLocal(
+    static Result<GitDB> initLocal(
             final Path dbDir,
             final String userName,
             final String userEmailAddress
-    ) throws IOException {
+    ) {
         return LocalGitDB.init(dbDir, userName, userEmailAddress);
     }
 
@@ -59,7 +58,7 @@ public interface GitDB {
      * @param userEmailAddress the user email address
      * @return a GitDB instance for the local gitdb
      */
-    static GitDB openLocal(final Path dbDir, final String userName, final String userEmailAddress) {
+    static Result<GitDB> openLocal(final Path dbDir, final String userName, final String userEmailAddress) {
         return LocalGitDB.open(dbDir, userName, userEmailAddress);
     }
 
@@ -67,9 +66,8 @@ public interface GitDB {
      * Select the named branch.
      *
      * @param name the branch to select
-     * @return an Optional containing the branch if it exists
+     * @return an Result Maybe containing the branch if it exists
-     * @throws IOException if there is an error accessing the branch name
      */
-    Optional<GitDBBranch> branch(String name) throws IOException;
+    Result<Maybe<GitDBBranch>> branch(String name);
 
 }

src/main/java/net/kemitix/gitdb/GitDBBranch.java

@@ -22,9 +22,8 @@
 package net.kemitix.gitdb;
 
 import com.github.zafarkhaja.semver.Version;
-
+import net.kemitix.mon.maybe.Maybe;
-import java.io.IOException;
+import net.kemitix.mon.result.Result;
-import java.util.Optional;
 
 /**
  * API for interacting with a branch in a GirDB.
@@ -38,9 +37,8 @@ public interface GitDBBranch {
      *
      * @param key the key to lookup
      * @return an Optional containing the value, if it exists, or empty if not
-     * @throws IOException if there was an error reading the value
      */
-    Optional<String> get(String key) throws IOException;
+    Result<Maybe<String>> get(String key);
 
     /**
      * Put a value into the store for the key.
@@ -48,18 +46,16 @@ public interface GitDBBranch {
      * @param key   the key to place the value under
      * @param value the value (must be Serializable)
      * @return an updated branch containing the new key/value
-     * @throws IOException if there was an error writing the key/value
      */
-    GitDBBranch put(String key, String value) throws IOException;
+    Result<GitDBBranch> put(String key, String value);
 
     /**
      * Removes a key and its value from the store.
      *
      * @param key the key to remove
      * @return an updated branch without the key, or the original if the key was not found
-     * @throws IOException if there was an error removing the key/value
      */
-    GitDBBranch remove(String key) throws IOException;
+    Result<GitDBBranch> remove(String key);
 
     /**
      * Returns the GitDB format for the current branch.
@@ -67,8 +63,7 @@ public interface GitDBBranch {
      * <p>Different branches can have different versions.</p>
      *
      * @return the format as per semantic versioning, i.e. "x.y.z" within an Optional
-     * @throws IOException error reading version
      */
-    Optional<Version> getFormatVersion() throws IOException;
+    Result<Maybe<Version>> getFormatVersion();
 
 }

src/main/java/net/kemitix/gitdb/impl/CommitWriter.java

@@ -21,10 +21,9 @@
 
 package net.kemitix.gitdb.impl;
 
+import net.kemitix.mon.result.Result;
 import org.eclipse.jgit.lib.*;
 
-import java.io.IOException;
-
 /**
  * Commits Key/Value updates into the Git Repository.
  *
@@ -52,15 +51,14 @@ class CommitWriter {
      * @param userName         the user name
      * @param userEmailAddress the user email address
      * @return the id of the commit
-     * @throws IOException if there is an error writing the value
      */
-    ObjectId write(
+    Result<ObjectId> write(
             final ObjectId treeId,
             final ObjectId parentId,
             final String message,
             final String userName,
             final String userEmailAddress
-    ) throws IOException {
+    ) {
         final CommitBuilder commitBuilder = new CommitBuilder();
         commitBuilder.setTreeId(treeId);
         commitBuilder.setMessage(message);
@@ -68,7 +66,7 @@ class CommitWriter {
         commitBuilder.setAuthor(ident);
         commitBuilder.setCommitter(ident);
         commitBuilder.setParentId(parentId);
-        return objectInserter.insert(commitBuilder);
+        return Result.of(() -> objectInserter.insert(commitBuilder));
     }
 
     /**
@@ -82,15 +80,14 @@ class CommitWriter {
      * @param userName         the user name
      * @param userEmailAddress the user email address
      * @return the id of the commit
-     * @throws IOException if there is an error writing the value
      */
-    ObjectId write(
+    Result<ObjectId> write(
             final ObjectId treeId,
             final Ref branchRef,
             final String message,
             final String userName,
             final String userEmailAddress
-    ) throws IOException {
+    ) {
         return write(treeId, branchRef.getObjectId(), message, userName, userEmailAddress);
     }
 }

src/main/java/net/kemitix/gitdb/impl/GitDBBranchImpl.java

@@ -25,12 +25,12 @@ import com.github.zafarkhaja.semver.Version;
 import lombok.AccessLevel;
 import lombok.RequiredArgsConstructor;
 import net.kemitix.gitdb.GitDBBranch;
+import net.kemitix.mon.maybe.Maybe;
+import net.kemitix.mon.result.Result;
 import org.eclipse.jgit.lib.ObjectId;
 import org.eclipse.jgit.lib.Ref;
 import org.eclipse.jgit.lib.Repository;
 
-import java.io.IOException;
-import java.util.Optional;
 import java.util.function.Function;
 
 /**
@@ -48,15 +48,6 @@ class GitDBBranchImpl implements GitDBBranch {
     private final String userEmailAddress;
     private final String name;
 
-    private static GitDBBranch select(
-            final Ref branchRef,
-            final GitDBRepo gitDBRepo,
-            final String userName,
-            final String userEmailAddress
-    ) {
-        return new GitDBBranchImpl(branchRef, gitDBRepo, userName, userEmailAddress, branchRef.getName());
-    }
-
     /**
      * Initialise the creation of new GitDBBranch instances.
      *
@@ -65,7 +56,7 @@ class GitDBBranchImpl implements GitDBBranch {
      * @param userEmailAddress the user's email address to record against changes
      * @return a Function for creating a GitDBBranch when supplied with a Ref for a branch
      */
-    static Function<Ref, GitDBBranch> init(
+    static Function<Ref, Result<GitDBBranch>> init(
             final Repository repository,
             final String userName,
             final String userEmailAddress
@@ -73,38 +64,52 @@ class GitDBBranchImpl implements GitDBBranch {
         return ref -> select(ref, new GitDBRepo(repository), userName, userEmailAddress);
     }
 
+    private static Result<GitDBBranch> select(
+            final Ref branchRef,
+            final GitDBRepo gitDBRepo,
+            final String userName,
+            final String userEmailAddress
+    ) {
+        return Result.ok(new GitDBBranchImpl(branchRef, gitDBRepo, userName, userEmailAddress, branchRef.getName()));
+    }
+
     @Override
-    public Optional<String> get(final String key) throws IOException {
+    public Result<Maybe<String>> get(final String key) {
         return gitDBRepo.readValue(branchRef, KEY_PREFIX + key);
     }
 
     @Override
-    public GitDBBranch put(final String key, final String value) throws IOException {
+    public Result<GitDBBranch> put(final String key, final String value) {
-        final ObjectId newTree = gitDBRepo.writeValue(branchRef, KEY_PREFIX + key, value);
         final String message = String.format("Add key [%s] = [%s]", key, value);
-        final Ref newBranch = gitDBRepo.writeCommit(branchRef, newTree, message, userName, userEmailAddress);
+        return gitDBRepo.writeValue(branchRef, KEY_PREFIX + key, value)
-        return select(newBranch, gitDBRepo, userName, userEmailAddress);
+                .flatMap(nt -> gitDBRepo.writeCommit(branchRef, nt, message, userName, userEmailAddress))
+                .flatMap(nb -> select(nb, gitDBRepo, userName, userEmailAddress));
     }
 
     @Override
-    public GitDBBranch remove(final String key) throws IOException {
+    public Result<GitDBBranch> remove(final String key) {
-        final Optional<ObjectId> newTree = gitDBRepo.removeKey(branchRef, KEY_PREFIX + key);
+        return gitDBRepo.removeKey(branchRef, KEY_PREFIX + key).flatMap(treeId ->
-        if (newTree.isPresent()) {
+                writeRemoveKeyCommit(key, treeId)
-            final Ref newBranch =
+                        .map(selectUpdatedBranch())
-                    gitDBRepo.writeCommit(
+                        .orElse(Result.ok(this)));
-                            branchRef, newTree.get(),
+    }
-                            String.format("Remove Key [%s]", key),
+
-                            userName,
+    private Maybe<Result<Ref>> writeRemoveKeyCommit(final String key, final Maybe<ObjectId> idMaybe) {
-                            userEmailAddress);
+        return idMaybe.map(objectId -> {
-            return select(newBranch, gitDBRepo, userName, userEmailAddress);
+            final String message = String.format("Remove Key [%s]", key);
-        }
+            return gitDBRepo.writeCommit(branchRef, objectId, message, userName, userEmailAddress);
-        return this;
+        });
+    }
+
+    private Function<Result<Ref>, Result<GitDBBranch>> selectUpdatedBranch() {
+        return refResult -> refResult.flatMap(ref ->
+                select(ref, gitDBRepo, userName, userEmailAddress));
     }
 
     @Override
-    public Optional<Version> getFormatVersion() throws IOException {
+    public Result<Maybe<Version>> getFormatVersion() {
         return gitDBRepo.readValue(branchRef, "GitDB.Version")
-                .map(Version::valueOf);
+                .map(version -> version.map(Version::valueOf));
     }
 
 }

src/main/java/net/kemitix/gitdb/impl/GitDBRepo.java

@@ -21,14 +21,14 @@
 
 package net.kemitix.gitdb.impl;
 
-import lombok.val;
+import net.kemitix.mon.maybe.Maybe;
+import net.kemitix.mon.result.Result;
 import org.eclipse.jgit.lib.ObjectId;
 import org.eclipse.jgit.lib.Ref;
 import org.eclipse.jgit.lib.Repository;
 
-import java.io.IOException;
 import java.nio.charset.StandardCharsets;
-import java.util.Optional;
+import java.util.stream.Stream;
 
 /**
  * Wrapper for interacting with the GitDB Repository.
@@ -47,7 +47,7 @@ class GitDBRepo {
     /**
      * Creates a new instance of this class.
      *
-     * @param repository       the Git Repository
+     * @param repository the Git Repository
      */
     GitDBRepo(final Repository repository) {
         this.repository = repository;
@@ -64,56 +64,35 @@ class GitDBRepo {
      * @param key     the key to insert
      * @param valueId id of the value
      * @return the id of the inserted tree
-     * @throws IOException the tree could not be stored
      */
-    ObjectId insertNewTree(
+    Result<ObjectId> insertNewTree(
             final String key,
             final ObjectId valueId
-    ) throws IOException {
+    ) {
         return keyWriter.writeFirst(key, valueId);
     }
 
-    /**
-     * Insert a commit into the store, returning its unique id.
-     *
-     * @param treeId           id of the tree
-     * @param branchRef        the branch to commit to
-     * @param message          the message
-     * @param userName         the user name
-     * @param userEmailAddress the user email address
-     * @return the id of the commit
-     * @throws IOException the commit could not be stored
-     */
-    ObjectId insertCommit(
-            final ObjectId treeId,
-            final String message,
-            final String userName,
-            final String userEmailAddress,
-            final Ref branchRef
-    ) throws IOException {
-        return commitWriter.write(treeId, branchRef, message, userName, userEmailAddress);
-    }
-
     /**
      * Reads a value from the branch with the given key.
      *
      * @param branchRef the branch to select from
      * @param key       the key to get the value for
      * @return an Optional containing the value if found, or empty
-     * @throws IOException if there was an error reading the value
      */
-    Optional<String> readValue(
+    Result<Maybe<String>> readValue(
             final Ref branchRef,
             final String key
-    ) throws IOException {
+    ) {
-        val blob = new GitTreeReader(repository)
+        final GitTreeReader treeFilter = new GitTreeReader(repository).treeFilter(key);
-                .treeFilter(key)
+        return streamTree(branchRef, treeFilter).flatMap(s ->
-                .stream(branchRef)
+                Result.invert(s.findFirst()
-                .findFirst();
+                        .map(NamedRevBlob::blobAsString)
-        if (blob.isPresent()) {
+                        .map(Maybe::just)
-            return Optional.of(blob.get().blobAsString());
+                        .orElseGet(Maybe::nothing)));
-        }
+    }
-        return Optional.empty();
+
+    private Result<Stream<NamedRevBlob>> streamTree(final Ref branchRef, final GitTreeReader treeFilter) {
+        return treeFilter.stream(branchRef);
     }
 
     /**
@@ -125,11 +104,10 @@ class GitDBRepo {
      * @param key       the key to place the value under
      * @param value     the value
      * @return the id of the updated tree containing the update
-     * @throws IOException if there was an error writing the value
      */
-    ObjectId writeValue(final Ref branchRef, final String key, final String value) throws IOException {
+    Result<ObjectId> writeValue(final Ref branchRef, final String key, final String value) {
-        final ObjectId blob = valueWriter.write(value.getBytes(StandardCharsets.UTF_8));
+        return valueWriter.write(value.getBytes(StandardCharsets.UTF_8))
-        return keyWriter.write(key, blob, branchRef);
+                .flatMap(b -> keyWriter.write(key, b, branchRef));
     }
 
     /**
@@ -141,17 +119,37 @@ class GitDBRepo {
      * @param userName         the user name
      * @param userEmailAddress the user email address
      * @return the Ref of the updated branch
-     * @throws IOException if there was an error writing the branch
      */
-    Ref writeCommit(
+    Result<Ref> writeCommit(
             final Ref branchRef,
             final ObjectId tree,
             final String message,
             final String userName,
             final String userEmailAddress
-    ) throws IOException {
+    ) {
-        final ObjectId commitId = insertCommit(tree, message, userName, userEmailAddress, branchRef);
+        return insertCommit(tree, message, userName, userEmailAddress, branchRef)
-        return headWriter.write(branchRef.getName(), commitId);
+                .flatMap(cid -> Result.of(() ->
+                        headWriter.write(branchRef.getName(), cid)));
+    }
+
+    /**
+     * Insert a commit into the store, returning its unique id.
+     *
+     * @param treeId           id of the tree
+     * @param branchRef        the branch to commit to
+     * @param message          the message
+     * @param userName         the user name
+     * @param userEmailAddress the user email address
+     * @return the id of the commit
+     */
+    Result<ObjectId> insertCommit(
+            final ObjectId treeId,
+            final String message,
+            final String userName,
+            final String userEmailAddress,
+            final Ref branchRef
+    ) {
+        return commitWriter.write(treeId, branchRef, message, userName, userEmailAddress);
     }
 
     /**
@@ -162,14 +160,13 @@ class GitDBRepo {
      * @param initUser    the user name
      * @param initEmail   the user email address
      * @return the id of the commit
-     * @throws IOException if there was an error writing the commit
      */
-    ObjectId initialCommit(
+    Result<ObjectId> initialCommit(
             final ObjectId treeId,
             final String initMessage,
             final String initUser,
             final String initEmail
-    ) throws IOException {
+    ) {
         return commitWriter.write(treeId, ObjectId.zeroId(), initMessage, initUser, initEmail);
     }
 
@@ -182,9 +179,8 @@ class GitDBRepo {
      * @param key       the key to place the value under
      * @return an Optional containing the id of the updated tree containing the update, if the key was found, or an
      * empty Optional if there key was not found, the there was no changes made
-     * @throws IOException if there was an error writing the value
      */
-    Optional<ObjectId> removeKey(final Ref branchRef, final String key) throws IOException {
+    Result<Maybe<ObjectId>> removeKey(final Ref branchRef, final String key) {
         return keyRemover.remove(branchRef, key);
     }
 

src/main/java/net/kemitix/gitdb/impl/GitTreeReader.java

@@ -23,15 +23,20 @@ package net.kemitix.gitdb.impl;
 
 import lombok.AccessLevel;
 import lombok.RequiredArgsConstructor;
+import net.kemitix.mon.result.Result;
 import org.eclipse.jgit.lib.Ref;
 import org.eclipse.jgit.lib.Repository;
+import org.eclipse.jgit.revwalk.RevCommit;
+import org.eclipse.jgit.revwalk.RevTree;
 import org.eclipse.jgit.revwalk.RevWalk;
 import org.eclipse.jgit.treewalk.TreeWalk;
 import org.eclipse.jgit.treewalk.filter.PathFilter;
 import org.eclipse.jgit.treewalk.filter.TreeFilter;
 
-import java.io.IOException;
 import java.util.Optional;
+import java.util.concurrent.Callable;
+import java.util.function.Consumer;
+import java.util.function.Function;
 import java.util.stream.Stream;
 
 /**
@@ -51,23 +56,55 @@ class GitTreeReader {
      *
      * @param branchRef the branch to read
      * @return a stream of key/value pairs as NamedRevBlobs
-     * @throws IOException if there is an error reading the commit or walking the tree
      */
-    Stream<NamedRevBlob> stream(final Ref branchRef) throws IOException {
+    Result<Stream<NamedRevBlob>> stream(final Ref branchRef) {
         final TreeWalk treeWalk = new TreeWalk(repository);
         final RevWalk revWalk = new RevWalk(repository);
-        treeWalk.addTree(revWalk.parseCommit(branchRef.getObjectId()).getTree());
+        return Result.of(parseBranchCommit(branchRef, revWalk))
-        treeWalk.setRecursive(false);
+                .map(RevCommit::getTree)
-        Optional.ofNullable(treeFilter)
+                .flatMap(addTreeTo(treeWalk))
-                .ifPresent(treeWalk::setFilter);
+                .peek(disableRecursion(treeWalk))
-        final Stream.Builder<NamedRevBlob> builder = Stream.builder();
+                .peek(setTreeFilter(treeWalk))
-        while (treeWalk.next()) {
+                .flatMap(streamMatching(treeWalk, revWalk));
-            builder.add(new NamedRevBlob(
+    }
-                    treeWalk.getNameString(),
+
-                    revWalk.lookupBlob(treeWalk.getObjectId(0)),
+    private Function<Void, Result<Stream<NamedRevBlob>>> streamMatching(
-                    repository));
+            final TreeWalk treeWalk,
-        }
+            final RevWalk revWalk
-        return builder.build();
+    ) {
+        return x -> Result.of(() -> {
+            final Stream.Builder<NamedRevBlob> builder = Stream.builder();
+            while (treeWalk.next()) {
+                builder.add(namedRevBlob(treeWalk, revWalk));
+            }
+            return builder.build();
+        });
+    }
+
+    private NamedRevBlob namedRevBlob(TreeWalk treeWalk, RevWalk revWalk) {
+        return new NamedRevBlob(
+                treeWalk.getNameString(),
+                revWalk.lookupBlob(treeWalk.getObjectId(0)),
+                repository);
+    }
+
+    private Consumer<Void> setTreeFilter(TreeWalk treeWalk) {
+        return x -> Optional.ofNullable(treeFilter).ifPresent(treeWalk::setFilter);
+    }
+
+    private Consumer<Void> disableRecursion(TreeWalk treeWalk) {
+        return x -> treeWalk.setRecursive(false);
+    }
+
+    private Function<RevTree, Result<Void>> addTreeTo(TreeWalk treeWalk) {
+        return tree -> Result.of(() -> {
+            treeWalk.addTree(tree);
+            return null;
+        });
+    }
+
+    private Callable<RevCommit> parseBranchCommit(Ref branchRef, RevWalk revWalk) {
+        return () -> revWalk.parseCommit(branchRef.getObjectId());
     }
 
     /**
@@ -77,7 +114,7 @@ class GitTreeReader {
      * @return the GitTreeReader
      */
     GitTreeReader treeFilter(final String path) {
-        this.treeFilter = PathFilter.create(path);
+        treeFilter = PathFilter.create(path);
         return this;
     }
 

src/main/java/net/kemitix/gitdb/impl/HeadWriter.java

@@ -22,11 +22,11 @@
 package net.kemitix.gitdb.impl;
 
 import lombok.RequiredArgsConstructor;
+import net.kemitix.mon.result.Result;
 import org.eclipse.jgit.lib.ObjectId;
 import org.eclipse.jgit.lib.Ref;
 import org.eclipse.jgit.lib.Repository;
 
-import java.io.IOException;
 import java.nio.charset.StandardCharsets;
 import java.nio.file.Files;
 import java.nio.file.Path;
@@ -47,16 +47,17 @@ class HeadWriter {
      * @param branchName the branch name
      * @param commitId   the commit to point the branch at
      * @return the Ref of the new branch
-     * @throws IOException error writing branch head
      */
-    Ref write(final String branchName, final ObjectId commitId) throws IOException {
+    Result<Ref> write(final String branchName, final ObjectId commitId) {
         final Path branchRefPath = repository
                 .getDirectory()
                 .toPath()
                 .resolve(branchName)
                 .toAbsolutePath();
         final byte[] commitIdBytes = commitId.name().getBytes(StandardCharsets.UTF_8);
-        Files.write(branchRefPath, commitIdBytes);
+        return Result.of(() -> {
-        return repository.findRef(branchName);
+            Files.write(branchRefPath, commitIdBytes);
+            return repository.findRef(branchName);
+        });
     }
 }

src/main/java/net/kemitix/gitdb/impl/InitGitDBRepo.java

@@ -22,6 +22,7 @@
 package net.kemitix.gitdb.impl;
 
 import net.kemitix.gitdb.FormatVersion;
+import net.kemitix.mon.result.Result;
 import org.eclipse.jgit.lib.ObjectId;
 import org.eclipse.jgit.lib.Repository;
 import org.eclipse.jgit.lib.RepositoryCache;
@@ -50,35 +51,73 @@ class InitGitDBRepo {
      * Initialise a new GitDB repo.
      *
      * @param dbDir the directory to initialise the repo in
-     * @throws IOException if there is an error in creating the repo files
      */
-    static void create(final Path dbDir) throws IOException {
+    static Result<Void> create(final Path dbDir) {
         final InitGitDBRepo initRepo = new InitGitDBRepo();
-        final File validDbDir = initRepo.validDbDir(dbDir.toFile());
+        return initRepo.validDbDir(dbDir.toFile())
-        validDbDir.mkdirs();
+                .peek(File::mkdirs)
-        try (Repository repository = RepositoryCache.FileKey.exact(validDbDir, FS.DETECTED).open(false)) {
+                .flatMap(dir -> {
-            repository.create(true);
+                    try (Repository repository = RepositoryCache.FileKey.exact(dir, FS.DETECTED).open(false)) {
-            initRepo.createInitialBranchOnMaster(repository);
+                        repository.create(true);
-        }
+                        initRepo.createInitialBranchOnMaster(repository);
+                    } catch (IOException e) {
+                        return Result.error(e);
+                    }
+                    return Result.ok(null);
+                });
     }
 
-    private void createInitialBranchOnMaster(final Repository repository) throws IOException {
+    private Result<File> validDbDir(final File dbDir) {
+        return Result.ok(dbDir)
+                .flatMap(this::verifyIsNotAFile)
+                .flatMap(this::isEmptyIfExists);
+    }
+
+    private Result<Void> createInitialBranchOnMaster(final Repository repository) {
         final GitDBRepo repo = new GitDBRepo(repository);
-        final ValueWriter valueWriter = new ValueWriter(repository);
+        return new ValueWriter(repository)
-        final ObjectId objectId = valueWriter.write(new FormatVersion().toBytes());
+                .write(new FormatVersion().toBytes())
-        final ObjectId treeId = repo.insertNewTree(GIT_DB_VERSION, objectId);
+                .flatMap(oid -> repo.insertNewTree(GIT_DB_VERSION, oid))
-        final ObjectId commitId = repo.initialCommit(treeId, INIT_MESSAGE, INIT_USER, INIT_EMAIL);
+                .flatMap(tid -> repo.initialCommit(tid, INIT_MESSAGE, INIT_USER, INIT_EMAIL))
-        createBranch(repository, commitId, MASTER);
+                .flatMap(cid -> Result.of(() -> {
+                    createBranch(repository, cid, MASTER);
+                    return null;
+                }));
     }
 
-    private void createBranch(
+    private Result<File> verifyIsNotAFile(final File dbDir) {
+        if (dbDir.isFile()) {
+            return Result.error(new NotDirectoryException(dbDir.toString()));
+        }
+        return Result.ok(dbDir);
+    }
+
+    private Result<File> isEmptyIfExists(final File dbDir) {
+        if (dbDir.exists()) {
+            return Result.of(() -> {
+                        try (DirectoryStream<Path> directoryStream = Files.newDirectoryStream(dbDir.toPath())) {
+                            if (directoryStream.iterator().hasNext()) {
+                                throw new DirectoryNotEmptyException(dbDir.toString());
+                            }
+                        }
+                        return dbDir;
+                    }
+            );
+        }
+        return Result.ok(dbDir);
+    }
+
+    private Result<Void> createBranch(
             final Repository repository,
             final ObjectId commitId,
             final String branchName
-    ) throws IOException {
+    ) {
         final Path branchRefPath = branchRefPath(repository, branchName);
         final byte[] commitIdBytes = commitId.name().getBytes(StandardCharsets.UTF_8);
-        Files.write(branchRefPath, commitIdBytes);
+        return Result.of(() -> {
+            Files.write(branchRefPath, commitIdBytes);
+            return null;
+        });
     }
 
     private Path branchRefPath(
@@ -90,26 +129,4 @@ class InitGitDBRepo {
                 .resolve(String.format(REFS_HEADS_FORMAT, branchName))
                 .toAbsolutePath();
     }
-
-    private File validDbDir(final File dbDir) throws IOException {
-        verifyIsNotAFile(dbDir);
-        if (dbDir.exists()) {
-            verifyIsEmpty(dbDir);
-        }
-        return dbDir;
-    }
-
-    private void verifyIsEmpty(final File dbDir) throws IOException {
-        try (DirectoryStream<Path> directoryStream = Files.newDirectoryStream(dbDir.toPath())) {
-            if (directoryStream.iterator().hasNext()) {
-                throw new DirectoryNotEmptyException(dbDir.toString());
-            }
-        }
-    }
-
-    private void verifyIsNotAFile(final File dbDir) throws NotDirectoryException {
-        if (dbDir.isFile()) {
-            throw new NotDirectoryException(dbDir.toString());
-        }
-    }
 }

src/main/java/net/kemitix/gitdb/impl/KeyRemover.java

@@ -22,10 +22,11 @@
 package net.kemitix.gitdb.impl;
 
 import lombok.RequiredArgsConstructor;
+import net.kemitix.mon.maybe.Maybe;
+import net.kemitix.mon.result.Result;
 import org.eclipse.jgit.lib.*;
 
 import java.io.IOException;
-import java.util.Optional;
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.function.Consumer;
 import java.util.function.Predicate;
@@ -40,6 +41,24 @@ class KeyRemover {
 
     private final Repository repository;
 
+    /**
+     * Remove a key from the repository.
+     *
+     * @param branchRef the branch to update
+     * @param key       the key to remove
+     * @return the id of the updated tree
+     */
+    Result<Maybe<ObjectId>> remove(final Ref branchRef, final String key) {
+        final TreeFormatter treeFormatter = new TreeFormatter();
+        final AtomicBoolean removed = new AtomicBoolean(false);
+        new GitTreeReader(repository)
+                .stream(branchRef)
+                .peek(s -> s.peek(flagIfFound(key, removed))
+                        .filter(isNotKey(key))
+                        .forEach(addToTree(treeFormatter)));
+        return insertTree(treeFormatter).maybe(oi -> removed.get());
+    }
+
     /**
      * Sets the boolean to true if the key matches a NamedRevBlob's name.
      *
@@ -75,38 +94,17 @@ class KeyRemover {
         return item -> treeFormatter.append(item.getName(), item.getRevBlob());
     }
 
-    /**
-     * Remove a key from the repository.
-     *
-     * @param branchRef the branch to update
-     * @param key       the key to remove
-     * @return the id of the updated tree
-     * @throws IOException if there is an error writing the value
-     */
-    Optional<ObjectId> remove(final Ref branchRef, final String key) throws IOException {
-        final TreeFormatter treeFormatter = new TreeFormatter();
-        final AtomicBoolean removed = new AtomicBoolean(false);
-        new GitTreeReader(repository)
-                .stream(branchRef)
-                .peek(flagIfFound(key, removed))
-                .filter(isNotKey(key))
-                .forEach(addToTree(treeFormatter));
-        if (removed.get()) {
-            return Optional.of(insertTree(treeFormatter));
-        }
-        return Optional.empty();
-    }
-
     /**
      * Insert a tree into the repo, returning its id.
      *
      * @param treeFormatter the formatter containing the proposed tree's data.
      * @return the name of the tree object.
-     * @throws IOException the object could not be stored.
      */
-    private ObjectId insertTree(final TreeFormatter treeFormatter) throws IOException {
+    private Result<ObjectId> insertTree(final TreeFormatter treeFormatter) {
         try (ObjectInserter inserter = repository.getObjectDatabase().newInserter()) {
-            return inserter.insert(treeFormatter);
+            return Result.ok(inserter.insert(treeFormatter));
+        } catch (IOException e) {
+            return Result.error(e);
         }
     }
 }

src/main/java/net/kemitix/gitdb/impl/KeyWriter.java

@@ -21,10 +21,9 @@
 
 package net.kemitix.gitdb.impl;
 
+import net.kemitix.mon.result.Result;
 import org.eclipse.jgit.lib.*;
 
-import java.io.IOException;
-
 /**
  * Writes Keys into the Git Repository.
  *
@@ -48,42 +47,41 @@ class KeyWriter {
     /**
      * Write the first key into a new tree.
      *
-     * @param key the key
+     * @param key     the key
      * @param valueId the id of the value
      * @return the id of the new tree
-     * @throws IOException if there is an error writing the key
      */
-    ObjectId writeFirst(final String key, final ObjectId valueId) throws IOException {
+    Result<ObjectId> writeFirst(final String key, final ObjectId valueId) {
         return writeTree(key, valueId, new TreeFormatter());
     }
 
     /**
      * Write the key into a tree.
      *
-     * @param key the key
+     * @param key       the key
-     * @param valueId the id of the value
+     * @param valueId   the id of the value
      * @param branchRef the branch whose tree should be updated
      * @return the id of the updated tree
-     * @throws IOException if there is an error writing the key
      */
-    ObjectId write(final String key, final ObjectId valueId, final Ref branchRef) throws IOException {
+    Result<ObjectId> write(final String key, final ObjectId valueId, final Ref branchRef) {
-        return writeTree(key, valueId, getTreeFormatter(branchRef));
+        return getTreeFormatter(branchRef)
+                .flatMap(f -> writeTree(key, valueId, f));
     }
 
-    private TreeFormatter getTreeFormatter(final Ref branchRef) throws IOException {
+    private Result<TreeFormatter> getTreeFormatter(final Ref branchRef) {
         final TreeFormatter treeFormatter = new TreeFormatter();
         final GitTreeReader gitTreeReader = new GitTreeReader(repository);
-        gitTreeReader.stream(branchRef)
+        return gitTreeReader.stream(branchRef)
-                .forEach(item -> treeFormatter.append(item.getName(), item.getRevBlob()));
+                .peek(s -> s.forEach(item -> treeFormatter.append(item.getName(), item.getRevBlob())))
-        return treeFormatter;
+                .map(x -> treeFormatter);
     }
 
-    private ObjectId writeTree(
+    private Result<ObjectId> writeTree(
             final String key,
             final ObjectId valueId,
             final TreeFormatter treeFormatter
-    ) throws IOException {
+    ) {
         treeFormatter.append(key, FileMode.REGULAR_FILE, valueId);
-        return objectInserter.insert(treeFormatter);
+        return Result.of(() -> objectInserter.insert(treeFormatter));
     }
 }

src/main/java/net/kemitix/gitdb/impl/LocalGitDB.java

@@ -22,8 +22,8 @@
 package net.kemitix.gitdb.impl;
 
 import net.kemitix.gitdb.GitDB;
+import net.kemitix.mon.result.Result;
 
-import java.io.IOException;
 import java.nio.file.Path;
 
 /**
@@ -40,9 +40,8 @@ public interface LocalGitDB extends GitDB {
      * @param userName         the user name
      * @param userEmailAddress the user email address
      * @return a GitDB instance for the created local gitdb
-     * @throws IOException if there {@code dbDir} is a file or a non-empty directory
      */
-    static GitDB init(final Path dbDir, final String userName, final String userEmailAddress) throws IOException {
+    static Result<GitDB> init(final Path dbDir, final String userName, final String userEmailAddress) {
         return LocalGitDBImpl.init(dbDir, userName, userEmailAddress);
     }
 
@@ -54,7 +53,7 @@ public interface LocalGitDB extends GitDB {
      * @param userEmailAddress the user email address
      * @return a GitDB instance for the created local gitdb
      */
-    static GitDB open(final Path dbDir, final String userName, final String userEmailAddress) {
+    static Result<GitDB> open(final Path dbDir, final String userName, final String userEmailAddress) {
         return LocalGitDBImpl.open(dbDir, userName, userEmailAddress);
     }
 

src/main/java/net/kemitix/gitdb/impl/LocalGitDBImpl.java

@@ -24,12 +24,14 @@ package net.kemitix.gitdb.impl;
 import net.kemitix.gitdb.GitDB;
 import net.kemitix.gitdb.GitDBBranch;
 import net.kemitix.gitdb.InvalidRepositoryException;
+import net.kemitix.mon.maybe.Maybe;
+import net.kemitix.mon.result.Result;
 import org.eclipse.jgit.api.Git;
-import org.eclipse.jgit.lib.*;
+import org.eclipse.jgit.lib.Ref;
+import org.eclipse.jgit.lib.Repository;
 
 import java.io.IOException;
 import java.nio.file.Path;
-import java.util.Optional;
 import java.util.function.Function;
 
 /**
@@ -43,10 +45,8 @@ final class LocalGitDBImpl implements GitDB, LocalGitDB {
     private static final String ERROR_OPENING_REPOSITORY = "Error opening repository";
 
     private final Repository repository;
-    private final String userName;
-    private final String userEmailAddress;
 
-    private final Function<Ref, GitDBBranch> branchInit;
+    private final Function<Ref, Result<GitDBBranch>> branchInit;
 
     private LocalGitDBImpl(
             final Repository repository,
@@ -54,9 +54,7 @@ final class LocalGitDBImpl implements GitDB, LocalGitDB {
             final String userEmailAddress
     ) {
         this.repository = repository;
-        this.userName = userName;
+        branchInit = GitDBBranchImpl.init(this.repository, userName, userEmailAddress);
-        this.userEmailAddress = userEmailAddress;
-        branchInit = GitDBBranchImpl.init(this.repository, this.userName, this.userEmailAddress);
     }
 
     /**
@@ -66,15 +64,14 @@ final class LocalGitDBImpl implements GitDB, LocalGitDB {
      * @param userName         the user name
      * @param userEmailAddress the user email address
      * @return a GitDB instance for the created local gitdb
-     * @throws IOException if there {@code dbDir} is a file or a non-empty directory
      */
-    static GitDB init(
+    static Result<GitDB> init(
             final Path dbDir,
             final String userName,
             final String userEmailAddress
-    ) throws IOException {
+    ) {
-        InitGitDBRepo.create(dbDir);
+        return InitGitDBRepo.create(dbDir)
-        return open(dbDir, userName, userEmailAddress);
+                .flatMap(c -> open(dbDir, userName, userEmailAddress));
     }
 
     /**
@@ -85,25 +82,43 @@ final class LocalGitDBImpl implements GitDB, LocalGitDB {
      * @param userEmailAddress the user email address
      * @return a GitDB instance for the created local gitdb
      */
-    static GitDB open(
+    static Result<GitDB> open(
             final Path dbDir,
             final String userName,
             final String userEmailAddress
     ) {
+        return gitOpen(dbDir)
+                .map(Git::getRepository)
+                .maybe(Repository::isBare)
+                .flatMap(asErrorIfNotBare(dbDir))
+                .map(toLocalGitDB(userName, userEmailAddress));
+    }
+
+    private static Result<Git> gitOpen(Path dbDir) {
         try {
-            return Optional.of(Git.open(dbDir.toFile()))
+            return Result.ok(Git.open(dbDir.toFile()));
-                    .map(Git::getRepository)
-                    .filter(Repository::isBare)
-                    .map(repository -> new LocalGitDBImpl(repository, userName, userEmailAddress))
-                    .orElseThrow(() -> new InvalidRepositoryException(NOT_A_BARE_REPO, dbDir));
         } catch (IOException e) {
-            throw new InvalidRepositoryException(ERROR_OPENING_REPOSITORY, dbDir, e);
+            return Result.error(new InvalidRepositoryException(ERROR_OPENING_REPOSITORY, dbDir, e));
         }
     }
 
+    private static Function<Maybe<Repository>, Result<Repository>> asErrorIfNotBare(final Path dbDir) {
+        return maybe -> Result.fromMaybe(maybe, () -> new InvalidRepositoryException(NOT_A_BARE_REPO, dbDir));
+    }
+
+    private static Function<Repository, GitDB> toLocalGitDB(final String userName, final String userEmailAddress) {
+        return repository -> new LocalGitDBImpl(repository, userName, userEmailAddress);
+    }
+
     @Override
-    public Optional<GitDBBranch> branch(final String name) throws IOException {
+    public Result<Maybe<GitDBBranch>> branch(final String name) {
-        return Optional.ofNullable(repository.findRef(name)).map(branchInit);
+        try {
+            return Result.invert(Maybe.maybe(
+                    repository.findRef(name))
+                    .map(branchInit::apply));
+        } catch (IOException e) {
+            return Result.error(e);
+        }
     }
 
 }

src/main/java/net/kemitix/gitdb/impl/NamedRevBlob.java

@@ -24,7 +24,9 @@ package net.kemitix.gitdb.impl;
 import lombok.AccessLevel;
 import lombok.Getter;
 import lombok.RequiredArgsConstructor;
+import net.kemitix.mon.result.Result;
 import org.eclipse.jgit.lib.Constants;
+import org.eclipse.jgit.lib.ObjectLoader;
 import org.eclipse.jgit.lib.Repository;
 import org.eclipse.jgit.revwalk.RevBlob;
 
@@ -48,10 +50,15 @@ class NamedRevBlob {
      * Converts the blob to a String.
      *
      * @return a string
-     * @throws IOException of there was an error reading the blob
      */
-    String blobAsString() throws IOException {
+    Result<String> blobAsString() {
-        return new String(repository.open(revBlob.getId(), Constants.OBJ_BLOB).getBytes());
+        try {
+            return Result.ok(repository.open(revBlob.getId(), Constants.OBJ_BLOB))
+                    .map(ObjectLoader::getBytes)
+                    .map(String::new);
+        } catch (IOException e) {
+            return Result.error(e);
+        }
     }
 
 }

src/main/java/net/kemitix/gitdb/impl/ValueWriter.java

@@ -21,13 +21,12 @@
 
 package net.kemitix.gitdb.impl;
 
+import net.kemitix.mon.result.Result;
 import org.eclipse.jgit.lib.Constants;
 import org.eclipse.jgit.lib.ObjectId;
 import org.eclipse.jgit.lib.ObjectInserter;
 import org.eclipse.jgit.lib.Repository;
 
-import java.io.IOException;
-
 /**
  * Writes Values into the Git Repository.
  *
@@ -51,9 +50,8 @@ class ValueWriter {
      *
      * @param blob the value blob
      * @return the id of the value object
-     * @throws IOException if there is an error writing the value
      */
-    ObjectId write(final byte[] blob) throws IOException {
+    Result<ObjectId> write(final byte[] blob) {
-        return objectInserter.insert(Constants.OBJ_BLOB, blob);
+        return Result.of(() -> objectInserter.insert(Constants.OBJ_BLOB, blob));
     }
 }

src/test/java/net/kemitix/gitdb/test/GitDBTest.java

@@ -5,58 +5,53 @@ import net.kemitix.gitdb.FormatVersion;
 import net.kemitix.gitdb.GitDB;
 import net.kemitix.gitdb.GitDBBranch;
 import net.kemitix.gitdb.InvalidRepositoryException;
+import net.kemitix.mon.maybe.Maybe;
+import net.kemitix.mon.result.Result;
 import org.assertj.core.api.WithAssertions;
 import org.eclipse.jgit.api.Git;
 import org.eclipse.jgit.api.errors.GitAPIException;
 import org.eclipse.jgit.lib.Constants;
 import org.eclipse.jgit.lib.Repository;
 import org.junit.jupiter.api.Test;
-import org.junit.jupiter.api.extension.ExtendWith;
-import org.mockito.junit.jupiter.MockitoExtension;
 
-import java.io.BufferedReader;
 import java.io.IOException;
-import java.io.InputStreamReader;
-import java.io.PrintStream;
 import java.nio.file.DirectoryNotEmptyException;
 import java.nio.file.Files;
 import java.nio.file.NotDirectoryException;
 import java.nio.file.Path;
-import java.util.Optional;
 import java.util.UUID;
+import java.util.function.Consumer;
+import java.util.function.Function;
 import java.util.function.Supplier;
 
-import static org.assertj.core.api.Assumptions.assumeThat;
-
-@ExtendWith(MockitoExtension.class)
 class GitDBTest implements WithAssertions {
 
     private final Supplier<String> stringSupplier = UUID.randomUUID()::toString;
     private final String userName = stringSupplier.get();
     private final String userEmailAddress = stringSupplier.get();
 
-    private static void tree(final Path dbDir, final PrintStream out) throws IOException {
-        final Process treeProcess = new ProcessBuilder("tree", dbDir.toString()).start();
-        try (final BufferedReader reader = new BufferedReader(new InputStreamReader(treeProcess.getInputStream()))) {
-            String line;
-            while (null != (line = reader.readLine())) {
-                out.println("line = " + line);
-            }
-        }
-    }
-
     // When initialising a repo in a dir that doesn't exist then a bare repo is created
     @Test
     void initRepo_whenDirNotExist_thenCreateBareRepo() throws IOException {
         //given
         final Path dir = dirDoesNotExist();
         //when
-        final GitDB gitDB = GitDB.initLocal(dir, userName, userEmailAddress);
+        final Result<GitDB> gitDB = GitDB.initLocal(dir, userName, userEmailAddress);
         //then
-        assertThat(gitDB).isNotNull();
+        assertThatResultIsOkay(gitDB);
         assertThatIsBareRepo(dir);
     }
 
+    private Path dirDoesNotExist() throws IOException {
+        final Path directory = Files.createTempDirectory("gitdb");
+        Files.delete(directory);
+        return directory;
+    }
+
+    private <T> void assertThatResultIsOkay(final Result<T> result) {
+        assertThat(result.isOkay()).isTrue();
+    }
+
     private void assertThatIsBareRepo(final Path dbDir) throws IOException {
         final Git git = Git.open(dbDir.toFile());
         final Repository repository = git.getRepository();
@@ -65,56 +60,64 @@ class GitDBTest implements WithAssertions {
         assertThat(repository.getDirectory()).isEqualTo(dbDir.toFile());
     }
 
-    private Path dirDoesNotExist() throws IOException {
-        final Path directory = Files.createTempDirectory("gitdb");
-        Files.delete(directory);
-        return directory;
-    }
-
     // When initialising a repo in a dir that is a file then an exception is thrown
     @Test
     void initRepo_whenDirIsFile_thenThrowException() throws IOException {
         //given
         final Path dir = fileExists();
+        //when
+        final Result<GitDB> gitDBResult = GitDB.initLocal(dir, userName, userEmailAddress);
         //then
-        assertThatExceptionOfType(NotDirectoryException.class)
+        gitDBResult.match(
-                .isThrownBy(() -> GitDB.initLocal(dir, userName, userEmailAddress))
+                failOnSuccess("Is a file not a directory"),
-                .withMessageContaining(dir.toString());
+                error -> assertThat(error)
+                        .isInstanceOf(NotDirectoryException.class)
+                        .hasMessageContaining(dir.toString())
+        );
     }
 
     private Path fileExists() throws IOException {
         return Files.createTempFile("gitdb", "file");
     }
 
+    private <T> Consumer<T> failOnSuccess(String message) {
+        return success -> fail(message);
+    }
+
     // When initialising a repo in a non-empty dir then an exception is thrown
     @Test
     void initRepo_whenNotEmptyDir_thenThrowException() throws IOException {
         //given
         final Path dir = dirExists();
         filesExistIn(dir);
+        //when
+        final Result<GitDB> gitDBResult = GitDB.initLocal(dir, userName, userEmailAddress);
         //then
-        assertThatExceptionOfType(DirectoryNotEmptyException.class)
+        gitDBResult.match(
-                .isThrownBy(() -> GitDB.initLocal(dir, userName, userEmailAddress))
+                failOnSuccess("Directory is not empty"),
-                .withMessageContaining(dir.toString());
+                error -> assertThat(error)
-    }
+                        .isInstanceOf(DirectoryNotEmptyException.class)
-
+                        .hasMessageContaining(dir.toString())
-    private void filesExistIn(final Path dir) throws IOException {
+        );
-        Files.createTempFile(dir, "gitdb", "file");
     }
 
     private Path dirExists() throws IOException {
         return Files.createTempDirectory("gitdb");
     }
 
+    private void filesExistIn(final Path dir) throws IOException {
+        Files.createTempFile(dir, "gitdb", "file");
+    }
+
     // When initialising a repo in a empty dir then a bare repo is created
     @Test
     void initRepo_whenEmptyDir_thenCreateBareRepo() throws IOException {
         //given
         final Path dir = dirExists();
         //when
-        final GitDB gitDB = GitDB.initLocal(dir, userName, userEmailAddress);
+        final Result<GitDB> gitDB = GitDB.initLocal(dir, userName, userEmailAddress);
         //then
-        assertThat(gitDB).isNotNull();
+        assertThatResultIsOkay(gitDB);
         assertThatIsBareRepo(dir);
     }
 
@@ -123,10 +126,16 @@ class GitDBTest implements WithAssertions {
     void openRepo_NotBareRepo_thenThrowException() throws IOException {
         //given
         final Path dir = dirExists();
+        //when
+        final Result<GitDB> gitDBResult = GitDB.openLocal(dir, userName, userEmailAddress);
         //then
-        assertThatExceptionOfType(InvalidRepositoryException.class)
+        gitDBResult.match(
-                .isThrownBy(() -> GitDB.openLocal(dir, userName, userEmailAddress))
+                failOnSuccess("Not a bare repo"),
-                .withMessageContaining(dir.toString());
+                error -> assertThat(error)
+                        .isInstanceOf(InvalidRepositoryException.class)
+                        .hasMessageContaining(dir.toString())
+        );
+
     }
 
     // When opening a repo in a dir that is a file then an exception is thrown
@@ -134,10 +143,15 @@ class GitDBTest implements WithAssertions {
     void openRepo_whenDirIsFile_thenThrowException() throws IOException {
         //given
         final Path dir = fileExists();
+        //when
+        final Result<GitDB> gitDBResult = GitDB.openLocal(dir, userName, userEmailAddress);
         //then
-        assertThatExceptionOfType(InvalidRepositoryException.class)
+        gitDBResult.match(
-                .isThrownBy(() -> GitDB.openLocal(dir, userName, userEmailAddress))
+                failOnSuccess("Directory is a file"),
-                .withMessageContaining(dir.toString());
+                error -> assertThat(error)
+                        .isInstanceOf(InvalidRepositoryException.class)
+                        .hasMessageContaining(dir.toString())
+        );
     }
 
     // When opening a repo in a dir that doesn't exist then an exception is thrown
@@ -145,10 +159,15 @@ class GitDBTest implements WithAssertions {
     void openRepo_whenDirNotExist_thenThrowException() throws IOException {
         //given
         final Path dir = dirDoesNotExist();
+        //when
+        final Result<GitDB> gitDBResult = GitDB.openLocal(dir, userName, userEmailAddress);
         //then
-        assertThatExceptionOfType(InvalidRepositoryException.class)
+        gitDBResult.match(
-                .isThrownBy(() -> GitDB.openLocal(dir, userName, userEmailAddress))
+                failOnSuccess("Directory does not exist"),
-                .withMessageContaining(dir.toString());
+                error -> assertThat(error)
+                        .isInstanceOf(InvalidRepositoryException.class)
+                        .hasMessageContaining(dir.toString())
+        );
     }
 
     // When opening a repo in a dir that is not a bare repo then an exception is thrown
@@ -156,12 +175,17 @@ class GitDBTest implements WithAssertions {
     void openRepo_whenRepoNotBare_thenThrowException() throws IOException, GitAPIException {
         //given
         final Path dir = nonBareRepo();
+        //when
+        final Result<GitDB> gitDBResult = GitDB.openLocal(dir, userName, userEmailAddress);
         //then
-        assertThatExceptionOfType(InvalidRepositoryException.class)
+        gitDBResult.match(
-                .isThrownBy(() -> GitDB.openLocal(dir, userName, userEmailAddress))
+                failOnSuccess("Not a bare repo"),
-                .withMessageContaining("Invalid GitDB repo")
+                error -> assertThat(error)
-                .withMessageContaining("Not a bare repo")
+                        .isInstanceOf(InvalidRepositoryException.class)
-                .withMessageContaining(dir.toString());
+                        .hasMessageContaining("Invalid GitDB repo")
+                        .hasMessageContaining("Not a bare repo")
+                        .hasMessageContaining(dir.toString())
+        );
     }
 
     private Path nonBareRepo() throws IOException, GitAPIException {
@@ -176,9 +200,13 @@ class GitDBTest implements WithAssertions {
         //given
         final Path dir = gitDBRepoPath();
         //when
-        final GitDB gitDB = GitDB.openLocal(dir, userName, userEmailAddress);
+        final Result<GitDB> gitDB = GitDB.openLocal(dir, userName, userEmailAddress);
         //then
-        assertThat(gitDB).isNotNull();
+        assertThat(gitDB.isOkay()).isTrue();
+        gitDB.match(
+                success -> assertThat(success).isNotNull(),
+                error -> fail("did not open local repo")
+        );
     }
 
     private Path gitDBRepoPath() throws IOException {
@@ -189,144 +217,179 @@ class GitDBTest implements WithAssertions {
 
     // Given a valid GitDb handle
 
-    private GitDB gitDB(final Path dbDir) throws IOException {
+    // When select a branch that doesn't exist then an empty Optional is returned
+    @Test
+    void selectBranch_whenBranchNotExist_thenEmptyOptional() throws Throwable {
+        //given
+        final Result<GitDB> gitDb = gitDB(dirDoesNotExist());
+        //when
+        final Result<Maybe<GitDBBranch>> branch = gitDb.flatMap(selectBranch("unknown"));
+        //then
+        assertThat(branch.orElseThrow().toOptional()).isEmpty();
+    }
+
+    private Result<GitDB> gitDB(final Path dbDir) {
         return GitDB.initLocal(dbDir, userName, userEmailAddress);
     }
 
-    // When select a branch that doesn't exist then an empty Optional is returned
+    private Function<GitDB, Result<Maybe<GitDBBranch>>> selectBranch(final String branchName) {
-    @Test
+        return db -> db.branch(branchName);
-    void selectBranch_whenBranchNotExist_thenEmptyOptional() throws IOException {
-        //given
-        final GitDB gitDb = gitDB(dirDoesNotExist());
-        //when
-        final Optional<GitDBBranch> branch = gitDb.branch("unknown");
-        //then
-        assertThat(branch).isEmpty();
-    }
-
-    // When select a valid branch then a GitDbBranch is returned
-    @Test
-    void selectBranch_branchExists_thenReturnBranch() throws IOException {
-        //given
-        final Path dbDir = dirDoesNotExist();
-        final GitDB gitDb = gitDB(dbDir);
-        //when
-        final Optional<GitDBBranch> branch = gitDb.branch("master");
-        //then
-        assertThat(branch).as("Branch master exists").isNotEmpty();
     }
 
     // Given a valid GitDbBranch handle
 
-    private GitDBBranch gitDBBranch() throws IOException {
+    // When select a valid branch then a GitDbBranch is returned
-        final GitDB gitDB = gitDB(dirDoesNotExist());
+    @Test
-        final Optional<GitDBBranch> branchOptional = gitDB.branch("master");
+    void selectBranch_branchExists_thenReturnBranch() throws Throwable {
-        assumeThat(branchOptional).isNotEmpty();
+        //given
-        return branchOptional.get();
+        final Path dbDir = dirDoesNotExist();
+        final Result<GitDB> gitDb = gitDB(dbDir);
+        //when
+        final Result<Maybe<GitDBBranch>> branch = gitDb.flatMap(selectBranch("master"));
+        //then
+        assertThat(branch.orElseThrow().toOptional()).as("Branch master exists").isNotEmpty();
     }
 
     // When getting a key that does not exist then return an empty Optional
     @Test
-    void getKey_whenKeyNotExist_thenReturnEmptyOptional() throws IOException, ClassNotFoundException {
+    void getKey_whenKeyNotExist_thenReturnEmptyOptional() {
         //given
         final GitDBBranch branch = gitDBBranch();
         //when
-        final Optional<String> value = branch.get("unknown");
+        final Result<Maybe<String>> value = branch.get("unknown");
         //then
-        assertThat(value).isEmpty();
+        value.match(
+                success -> assertThat(success.toOptional()).isEmpty(),
+                failOnError()
+        );
+    }
+
+    private GitDBBranch gitDBBranch() {
+        try {
+            return gitDB(dirDoesNotExist())
+                    .flatMap(selectBranch("master"))
+                    .orElseThrow().orElse(null);
+        } catch (Throwable throwable) {
+            throw new RuntimeException("Couldn't create master branch", throwable);
+        }
+    }
+
+    private Consumer<Throwable> failOnError() {
+        return error -> fail("Not an error");
     }
 
     // When getting the format version it matches expected
     @Test
-    void getVersionFormat_thenFormatIsSet() throws IOException {
+    void getVersionFormat_thenFormatIsSet() {
         //given
         final GitDBBranch gitDBBranch = gitDBBranch();
-        //when
-        final Optional<Version> formatVersion = gitDBBranch.getFormatVersion();
-        //then
         final Version version = new FormatVersion().getVersion();
-        assertThat(formatVersion).contains(version);
+        //when
-        assertThat(formatVersion.get()).isNotSameAs(version);
+        final Result<Maybe<Version>> formatVersion = gitDBBranch.getFormatVersion();
+        //then
+        formatVersion.match(
+                success -> success.peek(v -> assertThat(v).isEqualTo(version).isNotSameAs(version)),
+                failOnError()
+        );
     }
 
     // When putting a key/value pair then a GitDbBranch is returned
     @Test
-    void putValue_thenReturnUpdatedGitDBBranch() throws IOException {
+    void putValue_thenReturnUpdatedGitDBBranch() {
         //given
         final GitDBBranch originalBranch = gitDBBranch();
         //when
-        final GitDBBranch updatedBranch = originalBranch.put("key-name", "value");
+        final Result<GitDBBranch> updatedBranch = originalBranch.put("key-name", "value");
         //then
-        assertThat(updatedBranch).isNotNull();
+        updatedBranch.match(
-        assertThat(updatedBranch).isNotSameAs(originalBranch);
+                success -> assertThat(success).isNotNull().isNotSameAs(originalBranch),
+                failOnError()
+        );
     }
 
     // When getting a key that does exist then the value is returned inside an Optional
     @Test
-    void getKey_whenExists_thenReturnValueInOptional() throws IOException, ClassNotFoundException {
+    void getKey_whenExists_thenReturnValueInOptional() {
         //given
         final String key = stringSupplier.get();
         final String value = stringSupplier.get();
         final GitDBBranch originalBranch = gitDBBranch();
-        final GitDBBranch updatedBranch = originalBranch.put(key, value);
+        final Result<GitDBBranch> updatedBranch = originalBranch.put(key, value);
         //when
-        final Optional<String> result = updatedBranch.get(key);
+        final Result<Maybe<String>> result = updatedBranch.flatMap(b -> b.get(key));
         //then
-        assertThat(result).contains(value);
+        result.match(
+                success -> success.map(v -> assertThat(v).contains(value)),
+                failOnError()
+        );
     }
 
     // When removing a key that does not exist then the GitDbBranch is returned
     @Test
-    void removeKey_whenNotExist_thenReturnOriginal() throws IOException {
+    void removeKey_whenNotExist_thenReturnOriginal() {
         //given
         final GitDBBranch gitDBBranch = gitDBBranch();
         //when
-        final GitDBBranch result = gitDBBranch.remove("unknown");
+        final Result<GitDBBranch> result = gitDBBranch.remove("unknown");
         //then
-        assertThat(result).isSameAs(gitDBBranch);
+        result.match(
+                success -> assertThat(success).isSameAs(gitDBBranch),
+                failOnError()
+        );
     }
 
     // When removing a key that does exist then a GitDbBranch is returned
     @Test
-    void removeKey_whenExists_thenReturnUpdatedBranch() throws IOException {
+    void removeKey_whenExists_thenReturnUpdatedBranch() {
         //given
         final String key = stringSupplier.get();
         final String value = stringSupplier.get();
-        final GitDBBranch originalBranch = gitDBBranchWithKeyValue(key, value);
+        final Result<GitDBBranch> originalBranch = gitDBBranchWithKeyValue(key, value);
         //when
-        final GitDBBranch updatedBranch = originalBranch.remove(key);
+        final Result<GitDBBranch> updatedBranch = originalBranch.flatMap(b -> b.remove(key));
         //then
-        assertThat(updatedBranch).isNotSameAs(originalBranch);
+        updatedBranch.match(
+                success -> assertThat(success).isNotSameAs(originalBranch),
+                failOnError()
+        );
     }
 
-    private GitDBBranch gitDBBranchWithKeyValue(final String key, final String value) throws IOException {
+    private Result<GitDBBranch> gitDBBranchWithKeyValue(final String key, final String value) {
         return gitDBBranch().put(key, value);
     }
 
     // When removing a key that does exist then original GitDbBranch can still find it
     @Test
-    void removeKey_whenExists_thenOriginalCanStillFind() throws IOException {
+    void removeKey_whenExists_thenOriginalCanStillFind() {
         //given
         final String key = stringSupplier.get();
         final String value = stringSupplier.get();
-        final GitDBBranch originalBranch = gitDBBranchWithKeyValue(key, value);
+        final Result<GitDBBranch> originalBranch = gitDBBranchWithKeyValue(key, value);
         //when
-        final GitDBBranch updatedBranch = originalBranch.remove(key);
+        final Result<GitDBBranch> updatedBranch = originalBranch.flatMap(b -> b.remove(key));
         //then
-        assertThat(originalBranch.get(key)).contains(value);
+        originalBranch.flatMap(b -> b.get(key))
+                .match(
+                        success -> assertThat(success.toOptional()).contains(value),
+                        failOnError()
+                );
     }
 
     // When removing a key that does exist then the updated GitDbBranch can't find it
     @Test
-    void removeKey_whenExists_thenUpdatedCanNotFind() throws IOException {
+    void removeKey_whenExists_thenUpdatedCanNotFind() {
         //given
         final String key = stringSupplier.get();
         final String value = stringSupplier.get();
-        final GitDBBranch originalBranch = gitDBBranchWithKeyValue(key, value);
+        final Result<GitDBBranch> originalBranch = gitDBBranchWithKeyValue(key, value);
         //when
-        final GitDBBranch updatedBranch = originalBranch.remove(key);
+        final Result<GitDBBranch> updatedBranch = originalBranch.flatMap(b -> b.remove(key));
         //then
-        assertThat(updatedBranch.get(key)).isEmpty();
+        updatedBranch.flatMap(b -> b.get(key))
+                .match(
+                        success -> assertThat(success.toOptional()).isEmpty(),
+                        failOnError()
+                );
     }
 
 }