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handler_car.go
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handler_car.go
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package gateway
import (
"context"
"encoding/binary"
"errors"
"fmt"
"io"
"net/http"
"strconv"
"strings"
"time"
"github.com/cespare/xxhash/v2"
"github.com/ipfs/boxo/path"
"github.com/ipfs/go-cid"
"go.opentelemetry.io/otel/attribute"
"go.opentelemetry.io/otel/trace"
"go.uber.org/multierr"
)
const (
carRangeBytesKey = "entity-bytes"
carTerminalElementTypeKey = "dag-scope"
carVersionKey = "car-version"
carDuplicatesKey = "car-dups"
carOrderKey = "car-order"
)
// serveCAR returns a CAR stream for specific DAG+selector
func (i *handler) serveCAR(ctx context.Context, w http.ResponseWriter, r *http.Request, rq *requestData) bool {
ctx, span := spanTrace(ctx, "Handler.ServeCAR", trace.WithAttributes(attribute.String("path", rq.immutablePath.String())))
defer span.End()
ctx, cancel := context.WithCancel(ctx)
defer cancel()
params, err := buildCarParams(r, rq.responseParams)
if err != nil {
i.webError(w, r, err, http.StatusBadRequest)
return false
}
rootCid, lastSegment, err := getCarRootCidAndLastSegment(rq.immutablePath)
if err != nil {
i.webError(w, r, err, http.StatusInternalServerError)
return false
}
// Set Content-Disposition
var name string
if urlFilename := r.URL.Query().Get("filename"); urlFilename != "" {
name = urlFilename
} else {
name = rootCid.String()
if lastSegment != "" {
name += "_" + lastSegment
}
name += ".car"
}
setContentDispositionHeader(w, name, "attachment")
// Set Cache-Control (same logic as for a regular files)
addCacheControlHeaders(w, r, rq.contentPath, rq.ttl, rq.lastMod, rootCid, carResponseFormat)
// Generate the CAR Etag.
etag := getCarEtag(rq.immutablePath, params, rootCid)
w.Header().Set("Etag", etag)
// Terminate early if Etag matches. We cannot rely on handleIfNoneMatch since
// since it does not contain the parameters information we retrieve here.
if etagMatch(r.Header.Get("If-None-Match"), etag) {
w.WriteHeader(http.StatusNotModified)
return false
}
md, carFile, err := i.backend.GetCAR(ctx, rq.immutablePath, params)
if !i.handleRequestErrors(w, r, rq.contentPath, err) {
return false
}
defer carFile.Close()
setIpfsRootsHeader(w, rq, &md)
// Make it clear we don't support range-requests over a car stream
// Partial downloads and resumes should be handled using requests for
// sub-DAGs and IPLD selectors: https://github.com/ipfs/go-ipfs/issues/8769
w.Header().Set("Accept-Ranges", "none")
w.Header().Set("Content-Type", buildContentTypeFromCarParams(params))
w.Header().Set("X-Content-Type-Options", "nosniff") // no funny business in the browsers :^)
_, copyErr := io.Copy(w, carFile)
carErr := carFile.Close()
streamErr := multierr.Combine(carErr, copyErr)
if streamErr != nil {
// Update fail metric
i.carStreamFailMetric.WithLabelValues(rq.contentPath.Namespace()).Observe(time.Since(rq.begin).Seconds())
// We return error as a trailer, however it is not something browsers can access
// (https://github.com/mdn/browser-compat-data/issues/14703)
// Due to this, we suggest client always verify that
// the received CAR stream response is matching requested DAG selector
w.Header().Set("X-Stream-Error", streamErr.Error())
return false
}
// Update metrics
i.carStreamGetMetric.WithLabelValues(rq.contentPath.Namespace()).Observe(time.Since(rq.begin).Seconds())
return true
}
// buildCarParams returns CarParams based on the request, any optional parameters
// passed in URL, Accept header and the implicit defaults specific to boxo
// implementation, such as block order and duplicates status.
//
// If any of the optional content type parameters (e.g., CAR order or
// duplicates) are unspecified or empty, the function will automatically infer
// default values.
func buildCarParams(r *http.Request, contentTypeParams map[string]string) (CarParams, error) {
// URL query parameters
queryParams := r.URL.Query()
rangeStr, hasRange := queryParams.Get(carRangeBytesKey), queryParams.Has(carRangeBytesKey)
scopeStr, hasScope := queryParams.Get(carTerminalElementTypeKey), queryParams.Has(carTerminalElementTypeKey)
params := CarParams{}
if hasRange {
rng, err := NewDagByteRange(rangeStr)
if err != nil {
err = fmt.Errorf("invalid application/vnd.ipld.car entity-bytes URL parameter: %w", err)
return CarParams{}, err
}
params.Range = &rng
}
if hasScope {
switch s := DagScope(scopeStr); s {
case DagScopeEntity, DagScopeAll, DagScopeBlock:
params.Scope = s
default:
err := fmt.Errorf("unsupported application/vnd.ipld.car dag-scope URL parameter: %q", scopeStr)
return CarParams{}, err
}
} else {
params.Scope = DagScopeAll
}
// application/vnd.ipld.car content type parameters from Accept header
// Get CAR version, duplicates and order from the query parameters and override
// with parameters from Accept header if they exist, since they have priority.
versionStr := queryParams.Get(carVersionKey)
duplicatesStr := queryParams.Get(carDuplicatesKey)
orderStr := queryParams.Get(carOrderKey)
if v, ok := contentTypeParams["version"]; ok {
versionStr = v
}
if v, ok := contentTypeParams["order"]; ok {
orderStr = v
}
if v, ok := contentTypeParams["dups"]; ok {
duplicatesStr = v
}
// version of CAR format
switch versionStr {
case "": // noop, client does not care about version
case "1": // noop, we support this
default:
return CarParams{}, errors.New("unsupported application/vnd.ipld.car version: only version=1 is supported")
}
// optional order from IPIP-412
if order := DagOrder(orderStr); order != DagOrderUnspecified {
switch order {
case DagOrderUnknown, DagOrderDFS:
params.Order = order
default:
return CarParams{}, fmt.Errorf("unsupported application/vnd.ipld.car content type order parameter: %q", order)
}
} else {
// when order is not specified, we use DFS as the implicit default
// as this has always been the default behavior and we should not break
// legacy clients
params.Order = DagOrderDFS
}
// optional dups from IPIP-412
dups, err := NewDuplicateBlocksPolicy(duplicatesStr)
if err != nil {
return CarParams{}, err
}
if dups == DuplicateBlocksUnspecified {
// when duplicate block preference is not specified, we set it to
// false, as this has always been the default behavior, we should
// not break legacy clients, and responses to requests made via ?format=car
// should benefit from block deduplication
dups = DuplicateBlocksExcluded
}
params.Duplicates = dups
return params, nil
}
// buildContentTypeFromCarParams returns a string for Content-Type header.
// It does not change any values, CarParams are respected as-is.
func buildContentTypeFromCarParams(params CarParams) string {
h := strings.Builder{}
h.WriteString(carResponseFormat)
h.WriteString("; version=1")
if params.Order != DagOrderUnspecified {
h.WriteString("; order=")
h.WriteString(string(params.Order))
}
if params.Duplicates != DuplicateBlocksUnspecified {
h.WriteString("; dups=")
h.WriteString(params.Duplicates.String())
}
return h.String()
}
func getCarRootCidAndLastSegment(imPath path.ImmutablePath) (cid.Cid, string, error) {
imPathStr := imPath.String()
if !strings.HasPrefix(imPathStr, "/ipfs/") {
return cid.Undef, "", errors.New("path does not have /ipfs/ prefix")
}
firstSegment, remainingSegments, _ := strings.Cut(imPathStr[6:], "/")
rootCid, err := cid.Decode(firstSegment)
if err != nil {
return cid.Undef, "", err
}
// Almost like path.Base(remainingSegments), but without special case for empty strings.
lastSegment := strings.TrimRight(remainingSegments, "/")
if i := strings.LastIndex(lastSegment, "/"); i >= 0 {
lastSegment = lastSegment[i+1:]
}
return rootCid, lastSegment, err
}
func getCarEtag(imPath path.ImmutablePath, params CarParams, rootCid cid.Cid) string {
h := xxhash.New()
h.WriteString(imPath.String())
// be careful with hashes here, we need boundaries and per entry salt, we don't want a request that has:
// - scope = dfs
// and:
// - order = dfs
// to result in the same hash because if we just do hash(scope + order) they would both yield hash("dfs").
if params.Scope != DagScopeAll {
h.WriteString("\x00scope=")
h.WriteString(string(params.Scope))
}
// 'order' from IPIP-412 impact Etag only if set to something else
// than DFS (which is the implicit default)
if params.Order != DagOrderDFS {
h.WriteString("\x00order=")
h.WriteString(string(params.Order))
}
// 'dups' from IPIP-412 impact Etag only if 'y'
if dups := params.Duplicates; dups == DuplicateBlocksIncluded {
h.WriteString("\x00dups=y")
}
if params.Range != nil {
if params.Range.From != 0 || params.Range.To != nil {
h.WriteString("\x00range=")
var b [8]byte
binary.LittleEndian.PutUint64(b[:], uint64(params.Range.From))
h.Write(b[:])
if params.Range.To != nil {
binary.LittleEndian.PutUint64(b[:], uint64(*params.Range.To))
h.Write(b[:])
}
}
}
suffix := strconv.FormatUint(h.Sum64(), 32)
return `W/"` + rootCid.String() + ".car." + suffix + `"`
}