# go-ipfs Gateway GET flow

- Checks if unsupported `X-Ipfs-Gateway-Prefix` header is present (https://github.com/ipfs/go-ipfs/issues/7702)
- Does request have `uri` query parameter? (for navigator.registerProtocolHandler Web API support)
- bad request if param value is not a valid URL with `ipfs:` or `ipns:` scheme
- redirect to /scheme/cid?query=val
- Does request have `Service-Worker` header with value `Script`?
- bad request if URL path starts with `/ipfs` or `/ipns` (https://github.com/ipfs/go-ipfs/issues/4025)
- Check if content path is a valid IPFS path
- bad request with redirect if the path has redundant `/ipfs` prefix, e.g. /ipfs/ipfs/{cid}
- bad request if otherwise not valid
- Resolve path to final DAG node using Unixfs resolver (for the ETag)
- Service Unavailable if node is offline
- Not Found on all other errors
- Determine the response format
- Does request have `format` query parameter?
- if `format` is `raw` use `application/vnd.ipld.raw`
- if `format` is `car` use `application/vnd.ipld.car`
- Does request have `Accept` header?
- if header value starts with `application/vnd.ipld` then use this header value
- Otherwise use empty string, implying UnixFS
- Does request have `If-None-Match` header?
- Not Modified if value of header matches the final DAG node CID
- Get reader for the final DAG node
- Internal Service Error if fetching block fails
- Update metric `gw_first_content_block_get_latency_seconds` (with namespace of ipfs or ipns)
- Write user headers from config
- Set header `X-Ipfs-Path` to content path
- Set header `X-Ipfs-Roots` to list of logical roots (CIDs of each path segment)
- Internal Service Error if building root list fails
- Write the response
- If response format is empty then assume UnixFS
- Get node as files.Node via UnixFS service
- Not Found on any error
- If node is a file
- Set `Etag` header to CID (NOTE: looks up response format again)
- Check mutability of content path
- If mutable then don't set cache control headers, set `modtime` to `now`
- TODO: set Cache-Control based on TTL of IPNS/DNSLink: https://github.com/ipfs/go-ipfs/issues/1818#issuecomment-1015849462
- TODO: set Last-Modified based on /ipns/ publishing timestamp?
- If immutable then set `Cache-Control` header to `public, max-age=29030400, immutable`, set `modtime` to zero
- TODO: set Last-Modified? - TBD - /ipfs/ modification metadata is present in unixfs 1.5 https://github.com/ipfs/go-ipfs/issues/6920?
- Set `Content-Disposition` header to `attachment; filename={cid}.bin; filename*=UTF-8''{cid}.bin`
- Get file size
- Bad Gateway if size is unknown
- Determine explicit content type
- content type is `inode/symlink` if node is files.Symlink
- otherwise
- try Go's mime type detection on file extension
- otherwise use https://github.com/gabriel-vasile/mimetype (see https://github.com/ipfs/go-ipfs/issues/7252)
- Internal Server Error if mimetype detection fails
- rewind content seeker to start
- Internal Server Error if rewind fails
- if mime type starts with `text/html;` strip encoding to let browser detect (https://github.com/ipfs/go-ipfs/issues/2203)
- Set `Content-Type` header to detected type
- If HTTP status code is `OK` but there is a `Location` header then change status code to Moved Permanently
- Serve bytes via Go's `http.ServeContent`
- Update metric `gw_unixfs_file_get_duration_seconds` (with namespace of ipfs or ipns)
- If node is a directory
- Look for a file in the UnixFS named `index.html`
- Internal Server Error on error other than ErrNoLink
- If `index.html` found
- If content path doesn't end in a slash and request does not have `go-get` parameter with value `1`
- Found (302) redirect to original path with slash
- Internal Server Error if `index.html` is not a file
- Serve `index.html` as above
- Moved Permanently if response already has a `Location` header
- Set `Content-Type` header to `text/html`
- Set `ETag` header to `DirIndex-{asset hash}_CID-{cid}`
- Does request have `If-None-Match` header?
- Not Modified if value of header matches Etag header
- Return if request method is `HEAD`
- Iterate over all entries in the directory
- Attempt to find a size for the entry, ignore errors
- Resolve the path to the entry
- Internal Server Error on error
- Add entry to listing
- Internal Server Error if iteration failed
- Construct link to directory's parent entry
- Attempt to find a size for the directory, ignore errors
- Set template's `GatewayURL` field to `gw-hostname` key in context
- Serve bytes by executing listing template
- Internal Server Error if fail
- Update metric `gw_unixfs_gen_dir_listing_get_duration_seconds` (with namespace of ipfs or ipns)
- Internal Server Error otherwise
- If response format is `application/vnd.ipld.raw` then serve a raw block
- Get reader for the block again
- Internal Service Error if getting reader fails
- Read all bytes of block into memory
- Internal Service Error if reading fails
- Set `Content-Disposition` header to `attachment; filename={cid}.bin; filename*=UTF-8''{cid}.bin`
- Set `Etag` header to CID (NOTE: looks up response format again)
- Check mutability of content path
- If mutable then don't set cache control headers, set `modtime` to `now`
- TODO: set Cache-Control based on TTL of IPNS/DNSLink: https://github.com/ipfs/go-ipfs/issues/1818#issuecomment-1015849462
- TODO: set Last-Modified based on /ipns/ publishing timestamp?
- If immutable then set `Cache-Control` header to `public, max-age=29030400, immutable`, set `modtime` to zero
- TODO: set Last-Modified? - TBD - /ipfs/ modification metadata is present in unixfs 1.5 https://github.com/ipfs/go-ipfs/issues/6920?
- Set `Content-Type` header to `application/vnd.ipld.raw`
- Set `X-Content-Type-Options` header to `nosniff`
- Serve bytes via Go's `http.ServeContent`
- Update metric `gw_raw_block_get_duration_seconds` (with namespace of ipfs or ipns)
- If response format is `application/vnd.ipld.car` then serve a car
- Set `Content-Disposition` header to `attachment; filename={cid}.car; filename*=UTF-8''{cid}.car`
- Set `Etag` header to W/CID (because we can't guarantee byte-for-byte identical responses, since blocks may arrive from datastore in non-deterministic order)
- Does request have `If-None-Match` header?
- Not Modified if value of header matches Etag header
- Set `Accept-Ranges` header to `none` since we don't support range-requests over a car stream (see https://github.com/ipfs/go-ipfs/issues/8769)
- Set `Cache-Control` header to `no-cache, no-transform` to ensure fresh stream on retry
- Set `Content-Type` header to `application/vnd.ipld.car; version=1`
- Set `X-Content-Type-Options` header to `nosniff`
- Serve bytes using go-car Write (NOTE: no context)
- Set `X-Stream-Error` trailer to error if serving fails, and exit
- Update metric `gw_car_stream_get_duration_seconds` (with namespace of ipfs or ipns)
- Bad Request if response format is anything else