Documentation
¶
Overview ¶
Package blockstore implements the IPFS blockstore interface backed by a CAR file. This package provides two flavours of blockstore: ReadOnly and ReadWrite.
The ReadOnly blockstore provides a read-only random access from a given data payload either in unindexed CARv1 format or indexed/unindexed v2 format:
- ReadOnly.NewReadOnly can be used to instantiate a new read-only blockstore for a given CARv1 or CARv2 data payload with an optional index override.
- ReadOnly.OpenReadOnly can be used to instantiate a new read-only blockstore for a given CARv1 or CARv2 file with automatic index generation if the index is not present.
The ReadWrite blockstore allows writing and reading of the blocks concurrently. The user of this blockstore is responsible for calling ReadWrite.Finalize when finished writing blocks. Upon finalization, the instance can no longer be used for reading or writing blocks and will error if used. To continue reading the blocks users are encouraged to use ReadOnly blockstore instantiated from the same file path using OpenReadOnly. A user may resume reading/writing from files produced by an instance of ReadWrite blockstore. The resumption is attempted automatically, if the path passed to OpenReadWrite exists.
Note that the blockstore implementations in this package behave similarly to IPFS IdStore wrapper when given CIDs with multihash.IDENTITY code. More specifically, for CIDs with multhash.IDENTITY code: * blockstore.Has will always return true. * blockstore.Get will always succeed, returning the multihash digest of the given CID. * blockstore.GetSize will always succeed, returning the multihash digest length of the given CID. * blockstore.Put and blockstore.PutMany will always succeed without performing any operation unless car.StoreIdentityCIDs is enabled.
See: https://pkg.go.dev/github.com/ipfs/go-ipfs-blockstore#NewIdStore
Index ¶
- func AllowDuplicatePuts(allow bool) carv2.Option
- func UseWholeCIDs(enable bool) carv2.Option
- func WithAsyncErrorHandler(ctx context.Context, errHandler func(error)) context.Context
- func WriteAsCarV1(asCarV1 bool) carv2.Option
- type ReadOnly
- func (b *ReadOnly) AllKeysChan(ctx context.Context) (<-chan cid.Cid, error)
- func (b *ReadOnly) Close() error
- func (b *ReadOnly) DeleteBlock(_ context.Context, _ cid.Cid) error
- func (b *ReadOnly) Get(ctx context.Context, key cid.Cid) (blocks.Block, error)
- func (b *ReadOnly) GetSize(ctx context.Context, key cid.Cid) (int, error)
- func (b *ReadOnly) Has(ctx context.Context, key cid.Cid) (bool, error)
- func (b *ReadOnly) HashOnRead(bool)
- func (b *ReadOnly) Put(context.Context, blocks.Block) error
- func (b *ReadOnly) PutMany(context.Context, []blocks.Block) error
- func (b *ReadOnly) Roots() ([]cid.Cid, error)
- type ReadWrite
- func (b *ReadWrite) AllKeysChan(ctx context.Context) (<-chan cid.Cid, error)
- func (b *ReadWrite) DeleteBlock(_ context.Context, _ cid.Cid) error
- func (b *ReadWrite) Discard()
- func (b *ReadWrite) Finalize() error
- func (b *ReadWrite) Get(ctx context.Context, key cid.Cid) (blocks.Block, error)
- func (b *ReadWrite) GetSize(ctx context.Context, key cid.Cid) (int, error)
- func (b *ReadWrite) Has(ctx context.Context, key cid.Cid) (bool, error)
- func (b *ReadWrite) HashOnRead(enable bool)
- func (b *ReadWrite) Put(ctx context.Context, blk blocks.Block) error
- func (b *ReadWrite) PutMany(ctx context.Context, blks []blocks.Block) error
- func (b *ReadWrite) Roots() ([]cid.Cid, error)
Examples ¶
Constants ¶
This section is empty.
Variables ¶
This section is empty.
Functions ¶
func AllowDuplicatePuts ¶
AllowDuplicatePuts is a write option which makes a CAR blockstore not deduplicate blocks in Put and PutMany. The default is to deduplicate, which matches the current semantics of go-ipfs-blockstore v1.
Note that this option only affects the blockstore, and is ignored by the root go-car/v2 package.
func UseWholeCIDs ¶
UseWholeCIDs is a read option which makes a CAR blockstore identify blocks by whole CIDs, and not just their multihashes. The default is to use multihashes, which matches the current semantics of go-ipfs-blockstore v1.
Enabling this option affects a number of methods, including read-only ones:
• Get, Has, and HasSize will only return a block only if the entire CID is present in the CAR file.
• AllKeysChan will return the original whole CIDs, instead of with their multicodec set to "raw" to just provide multihashes.
• If AllowDuplicatePuts isn't set, Put and PutMany will deduplicate by the whole CID, allowing different CIDs with equal multihashes.
Note that this option only affects the blockstore, and is ignored by the root go-car/v2 package.
func WithAsyncErrorHandler ¶
WithAsyncErrorHandler returns a context with async error handling set to the given errHandler. Any errors that occur during asynchronous operations of AllKeysChan will be passed to the given handler.
func WriteAsCarV1 ¶ added in v2.2.0
WriteAsCarV1 is a write option which makes a CAR blockstore write the output as a CARv1 only, with no CARv2 header or index. Indexing is used internally during write but is discarded upon finalization.
Note that this option only affects the blockstore, and is ignored by the root go-car/v2 package.
Types ¶
type ReadOnly ¶
type ReadOnly struct {
// contains filtered or unexported fields
}
ReadOnly provides a read-only CAR Block Store.
func NewReadOnly ¶
NewReadOnly creates a new ReadOnly blockstore from the backing with a optional index as idx. This function accepts both CARv1 and CARv2 backing. The blockstore is instantiated with the given index if it is not nil.
Otherwise: * For a CARv1 backing an index is generated. * For a CARv2 backing an index is only generated if Header.HasIndex returns false.
There is no need to call ReadOnly.Close on instances returned by this function.
func OpenReadOnly ¶
OpenReadOnly opens a read-only blockstore from a CAR file (either v1 or v2), generating an index if it does not exist. Note, the generated index if the index does not exist is ephemeral and only stored in memory. See car.GenerateIndex and Index.Attach for persisting index onto a CAR file.
Example ¶
ExampleOpenReadOnly opens a read-only blockstore from a CARv1 file, and prints its root CIDs along with CID mapping to raw data size of blocks for first five sections in the CAR file.
package main
import (
"context"
"fmt"
carv2 "github.com/ipld/go-car/v2"
"github.com/ipld/go-car/v2/blockstore"
)
const cidPrintCount = 5
func main() {
// Open a new ReadOnly blockstore from a CARv1 file.
// Note, `OpenReadOnly` accepts bot CARv1 and CARv2 formats and transparently generate index
// in the background if necessary.
// This instance sets ZeroLengthSectionAsEOF option to treat zero sized sections in file as EOF.
robs, err := blockstore.OpenReadOnly("../testdata/sample-v1.car",
blockstore.UseWholeCIDs(true),
carv2.ZeroLengthSectionAsEOF(true),
)
if err != nil {
panic(err)
}
defer robs.Close()
// Print root CIDs.
roots, err := robs.Roots()
if err != nil {
panic(err)
}
fmt.Printf("Contains %v root CID(s):\n", len(roots))
for _, r := range roots {
fmt.Printf("\t%v\n", r)
}
ctx, cancel := context.WithCancel(context.Background())
defer cancel()
// Print the raw data size for the first 5 CIDs in the CAR file.
keysChan, err := robs.AllKeysChan(ctx)
if err != nil {
panic(err)
}
fmt.Printf("List of first %v CIDs and their raw data size:\n", cidPrintCount)
i := 1
for k := range keysChan {
if i > cidPrintCount {
cancel()
break
}
size, err := robs.GetSize(context.TODO(), k)
if err != nil {
panic(err)
}
fmt.Printf("\t%v -> %v bytes\n", k, size)
i++
}
}
Output: Contains 1 root CID(s): bafy2bzaced4ueelaegfs5fqu4tzsh6ywbbpfk3cxppupmxfdhbpbhzawfw5oy List of first 5 CIDs and their raw data size: bafy2bzaced4ueelaegfs5fqu4tzsh6ywbbpfk3cxppupmxfdhbpbhzawfw5oy -> 821 bytes bafy2bzaceaycv7jhaegckatnncu5yugzkrnzeqsppzegufr35lroxxnsnpspu -> 1053 bytes bafy2bzaceb62wdepofqu34afqhbcn4a7jziwblt2ih5hhqqm6zitd3qpzhdp4 -> 1094 bytes bafy2bzaceb3utcspm5jqcdqpih3ztbaztv7yunzkiyfq7up7xmokpxemwgu5u -> 1051 bytes bafy2bzacedjwekyjresrwjqj4n2r5bnuuu3klncgjo2r3slsp6wgqb37sz4ck -> 821 bytes
func (*ReadOnly) AllKeysChan ¶
AllKeysChan returns the list of keys in the CAR data payload. If the ctx is constructed using WithAsyncErrorHandler any errors that occur during asynchronous retrieval of CIDs will be passed to the error handler function set in context. Otherwise, errors will terminate the asynchronous operation silently.
See WithAsyncErrorHandler
func (*ReadOnly) Close ¶
Close closes the underlying reader if it was opened by OpenReadOnly. After this call, the blockstore can no longer be used.
Note that this call may block if any blockstore operations are currently in progress, including an AllKeysChan that hasn't been fully consumed or cancelled.
func (*ReadOnly) DeleteBlock ¶
DeleteBlock is unsupported and always errors.
func (*ReadOnly) Get ¶
Get gets a block corresponding to the given key. This function always returns the block for any given key with multihash.IDENTITY code unless the StoreIdentityCIDs option is on, in which case it will defer to the index to check for the existence of the block; the index may or may not contain identity CIDs included in this CAR, depending on whether StoreIdentityCIDs was on when the index was created. If the CAR is a CARv1 and StoreIdentityCIDs is on, then the index will contain identity CIDs and this will always return true.
func (*ReadOnly) Has ¶
Has indicates if the store contains a block that corresponds to the given key. This function always returns true for any given key with multihash.IDENTITY code unless the StoreIdentityCIDs option is on, in which case it will defer to the index to check for the existence of the block; the index may or may not contain identity CIDs included in this CAR, depending on whether StoreIdentityCIDs was on when the index was created. If the CAR is a CARv1 and StoreIdentityCIDs is on, then the index will contain identity CIDs and this will always return true.
func (*ReadOnly) HashOnRead ¶
HashOnRead is currently unimplemented; hashing on reads never happens.
type ReadWrite ¶
type ReadWrite struct {
// contains filtered or unexported fields
}
ReadWrite implements a blockstore that stores blocks in CARv2 format. Blocks put into the blockstore can be read back once they are successfully written. This implementation is preferable for a write-heavy workload. The blocks are written immediately on Put and PutAll calls, while the index is stored in memory and updated incrementally.
The Finalize function must be called once the putting blocks are finished. Upon calling Finalize header is finalized and index is written out. Once finalized, all read and write calls to this blockstore will result in errors.
func OpenReadWrite ¶
OpenReadWrite creates a new ReadWrite at the given path with a provided set of root CIDs and options.
ReadWrite.Finalize must be called once putting and reading blocks are no longer needed. Upon calling ReadWrite.Finalize the CARv2 header and index are written out onto the file and the backing file is closed. Once finalized, all read and write calls to this blockstore will result in errors. Note, ReadWrite.Finalize must be called on an open instance regardless of whether any blocks were put or not.
If a file at given path does not exist, the instantiation will write car.Pragma and data payload header (i.e. the inner CARv1 header) onto the file before returning.
When the given path already exists, the blockstore will attempt to resume from it. On resumption the existing data sections in file are re-indexed, allowing the caller to continue putting any remaining blocks without having to re-ingest blocks for which previous ReadWrite.Put returned successfully.
Resumption only works on files that were created by a previous instance of a ReadWrite blockstore. This means a file created as a result of a successful call to OpenReadWrite can be resumed from as long as write operations such as ReadWrite.Put, ReadWrite.PutMany returned successfully. On resumption the roots argument and WithDataPadding option must match the previous instantiation of ReadWrite blockstore that created the file. More explicitly, the file resuming from must:
- start with a complete CARv2 car.Pragma.
- contain a complete CARv1 data header with root CIDs matching the CIDs passed to the constructor, starting at offset optionally padded by WithDataPadding, followed by zero or more complete data sections. If any corrupt data sections are present the resumption will fail. Note, if set previously, the blockstore must use the same WithDataPadding option as before, since this option is used to locate the CARv1 data payload.
Note, resumption should be used with WithCidDeduplication, so that blocks that are successfully written into the file are not re-written. Unless, the user explicitly wants duplicate blocks.
Resuming from finalized files is allowed. However, resumption will regenerate the index regardless by scanning every existing block in file.
Example ¶
ExampleOpenReadWrite creates a read-write blockstore and puts
ctx, cancel := context.WithTimeout(context.Background(), time.Second)
defer cancel()
thisBlock := merkledag.NewRawNode([]byte("fish")).Block
thatBlock := merkledag.NewRawNode([]byte("lobster")).Block
andTheOtherBlock := merkledag.NewRawNode([]byte("barreleye")).Block
tdir, err := os.MkdirTemp(os.TempDir(), "example-*")
if err != nil {
panic(err)
}
dst := filepath.Join(tdir, "sample-rw-bs-v2.car")
roots := []cid.Cid{thisBlock.Cid(), thatBlock.Cid(), andTheOtherBlock.Cid()}
rwbs, err := blockstore.OpenReadWrite(dst, roots, carv2.UseDataPadding(1413), carv2.UseIndexPadding(42))
if err != nil {
panic(err)
}
// Put all blocks onto the blockstore.
blocks := []blocks.Block{thisBlock, thatBlock}
if err := rwbs.PutMany(ctx, blocks); err != nil {
panic(err)
}
fmt.Printf("Successfully wrote %v blocks into the blockstore.\n", len(blocks))
// Any blocks put can be read back using the same blockstore instance.
block, err := rwbs.Get(ctx, thatBlock.Cid())
if err != nil {
panic(err)
}
fmt.Printf("Read back block just put with raw value of `%v`.\n", string(block.RawData()))
// Finalize the blockstore to flush out the index and make a complete CARv2.
if err := rwbs.Finalize(); err != nil {
panic(err)
}
// Resume from the same file to add more blocks.
// Note the UseDataPadding and roots must match the values passed to the blockstore instance
// that created the original file. Otherwise, we cannot resume from the same file.
resumedRwbos, err := blockstore.OpenReadWrite(dst, roots, carv2.UseDataPadding(1413))
if err != nil {
panic(err)
}
// Put another block, appending it to the set of blocks that are written previously.
if err := resumedRwbos.Put(ctx, andTheOtherBlock); err != nil {
panic(err)
}
// Read back the the block put before resumption.
// Blocks previously put are present.
block, err = resumedRwbos.Get(ctx, thatBlock.Cid())
if err != nil {
panic(err)
}
fmt.Printf("Resumed blockstore contains blocks put previously with raw value of `%v`.\n", string(block.RawData()))
// Put an additional block to the CAR.
// Blocks put after resumption are also present.
block, err = resumedRwbos.Get(ctx, andTheOtherBlock.Cid())
if err != nil {
panic(err)
}
fmt.Printf("It also contains the block put after resumption with raw value of `%v`.\n", string(block.RawData()))
// Finalize the blockstore to flush out the index and make a complete CARv2.
// Note, Finalize must be called on an open ReadWrite blockstore to flush out a complete CARv2.
if err := resumedRwbos.Finalize(); err != nil {
panic(err)
}
Output: Successfully wrote 2 blocks into the blockstore. Read back block just put with raw value of `lobster`. Resumed blockstore contains blocks put previously with raw value of `lobster`. It also contains the block put after resumption with raw value of `barreleye`.
func OpenReadWriteFile ¶ added in v2.5.0
OpenReadWriteFile is similar as OpenReadWrite but lets you control the file lifecycle. You are responsible for closing the given file.
func (*ReadWrite) AllKeysChan ¶
func (*ReadWrite) Discard ¶
func (b *ReadWrite) Discard()
Discard closes this blockstore without finalizing its header and index. After this call, the blockstore can no longer be used.
Note that this call may block if any blockstore operations are currently in progress, including an AllKeysChan that hasn't been fully consumed or cancelled.
func (*ReadWrite) Finalize ¶
Finalize finalizes this blockstore by writing the CARv2 header, along with flattened index for more efficient subsequent read. After this call, the blockstore can no longer be used.
Source Files