Range header

The HTTP Range {{Glossary("request header")}} indicates the part of a resource that the server should return. Several parts can be requested at the same time in one Range header, and the server may send back these ranges in a multipart document. If the server sends back ranges, it uses the {{HTTPStatus("206", "206 Partial Content")}} status code for the response. If the ranges are invalid, the server returns the {{HTTPStatus("416", "416 Range Not Satisfiable")}} error.

A server that doesn’t support range requests may ignore the Range header and return the whole resource with a {{HTTPStatus("200")}} status code. Older browsers used a response header of {{HTTPHeader("Accept-Ranges", "Accept-Ranges: none")}} to disable features like ‘pause’ or ‘resume’ in download managers, but since a server ignoring the Range header has the same meaning as responding with Accept-Ranges: none, the header is rarely used in this way.

Currently only bytes units are registered which are offsets (zero-indexed & inclusive). If the requested data has a content coding applied, each byte range represents the encoded sequence of bytes, not the bytes that would be obtained after decoding.

The header is a CORS-safelisted request header when the directive specifies a single byte range.

Header type	`{{Glossary("Request header")}}`
`{{Glossary("Forbidden request header")}}`	No

Syntax

Range: <unit>=<range-start>-
Range: <unit>=<range-start>-<range-end>
Range: <unit>=<range-start>-<range-end>, …, <range-startN>-<range-endN>
Range: <unit>=-<suffix-length>

Directives

<unit>
- : The unit in which ranges are defined. Currently only bytes are a registered unit.
<range-start>
- : An integer in the given unit indicating the start position of the request range.
<range-end>
- : An integer in the given unit indicating the end position of the requested range. This value is optional and, if omitted, the end of the resource is used as the end of the range.
<suffix-length>
- : An integer indicating the number of units at the end of the resource to return.

Examples

The following examples show how to make requests using the Range header for CORS-safelisted requests, and for requesting multiple ranges. Other examples can be found in the HTTP range requests guide.

Single byte ranges and CORS-safelisted requests

The Range header is a CORS-safelisted request header when the value is a single byte range. This means that it can be used in cross-origin requests without triggering a preflight request, which is useful for requesting media and resuming downloads.

The following example requests the first 500 bytes of a resource:

Range: bytes=0-499

To request the second 500 bytes:

Range: bytes=500-999

Omitting the end position requests all remaining units of the resource, so the last 100 bytes of a resource with a length of 1000 bytes can be requested using:

Range: bytes=900-

Alternatively, if it’s unknown how large a resource is, the last n bytes can be requested using a suffix range of -n:

Range: bytes=-100

Requesting multiple ranges

Given a resource with a length of 10000 bytes, the following example requests three separate ranges; 200-999 (800 bytes), 2000-2499 (500 bytes), and finally 9500-. The ranges-specifier value 9500- omits an end position which indicates that all bytes from 9500 onward are part of the third range (500 bytes).

Range: bytes=200-999, 2000-2499, 9500-

This example requests the first 500 and last 500 bytes of the file. The request may be rejected by the server if these ranges overlap (if the requested resource was less than 1000 bytes long, for instance).

Range: bytes=0-499, -500

Checking if a server supports range requests

The following curl command makes a {{HTTPMethod("HEAD")}} request for an image:

curl -v --http1.1 -I https://i.imgur.com/z4d4kWk.jpg
# or using the OPTIONS method:
# curl -v --http1.1 -X OPTIONS https://i.imgur.com/z4d4kWk.jpg

This results in the following HTTP request:

HEAD /z4d4kWk.jpg HTTP/1.1
Host: i.imgur.com
User-Agent: curl/8.7.1
Accept: */*

The server responds with a 200 response, and the Accept-Ranges: bytes header is present (some headers are omitted for brevity):

HTTP/1.1 200 OK
Connection: keep-alive
Content-Length: 146515
Content-Type: image/jpeg
…
Accept-Ranges: bytes

Fetching a range from a blob URL

The blob: URL also supports range requests by using fetch().

const blob = new Blob(["Hello, world!"], { type: "text/plain" });
const url = URL.createObjectURL(blob);
fetch(url, {
  headers: {
    Range: "bytes=7-11",
  },
})
  .then((response) => response.text())
  .then((text) => console.log(text)); // "world"

Specifications

{{Specifications}}

Browser compatibility

{{Compat}}

docs.rodeo

MDN Web Docs mirror