What causes "UnsupportedMediaType" in quickwit-oss/quickwit?

Set the request `Content-Type` header to `application/json` (or `application/toml` / `application/yaml` to match the body encoding).

quickwit-oss/quickwit · error · UnsupportedMediaType

UnsupportedMediaType

Error message

UnsupportedMediaType

What it means

`UnsupportedMediaType` is a warp custom rejection raised in `extract_config_format` (quickwit/quickwit-serve/src/format.rs:105) when a REST handler that accepts an index/source/index-template config receives a `Content-Type` header whose MIME subtype is not `json`, `toml`, or `yaml`. Quickwit only knows how to deserialize the posted configuration body in those three formats, so any other content type is rejected with an HTTP 415 Unsupported Media Type response.

Solutions

Set the request `Content-Type` header to `application/json` (or `application/toml` / `application/yaml` to match the body encoding).
Ensure the body actually matches the declared Content-Type (JSON body with JSON header, TOML body with TOML header).
Avoid vendor MIME suffixes; use plain `application/json` rather than `application/vnd.api+json`, since only the bare subtype is matched.
If using a generated HTTP client, override the default content type for these config endpoints.

Example fix

// before
curl -X POST http://localhost:7280/indexes -H 'Content-Type: text/plain' --data-binary @index-config.yaml
// after
curl -X POST http://localhost:7280/indexes -H 'Content-Type: application/yaml' --data-binary @index-config.yaml

Defensive patterns

Strategy: validation

Validate before calling

// Client-side check before sending
const ALLOWED = new Set(['application/json', 'application/toml', 'application/yaml']);
if (!ALLOWED.has(contentType)) {
  throw new Error(`Content-Type must be one of ${[...ALLOWED]}, got: ${contentType}`);
}

Type guard

fn is_supported_config_content_type(content_type: &str) -> bool {
  matches!(
    content_type,
    "application/json" | "application/toml" | "application/yaml"
      | "text/yaml" | "text/x-yaml"
  )
}

Try / catch

// Client side: catch the 415 rejection and report the offending header
try {
  const res = await fetch(url, { method: 'POST', headers: { 'Content-Type': 'application/json' }, body });
  if (!res.ok) throw new Error(`HTTP ${res.status}: ${await res.text()}`);
} catch (e) {
  if (String(e).includes('415') || String(e).includes('UnsupportedMediaType')) {
    console.error('Set Content-Type to application/json, application/toml, or application/yaml');
  }
  throw e;
}

Prevention

Always set Content-Type explicitly when posting index/source/template configs; never rely on HTTP client defaults.
Match the header to the actual body encoding (JSON body -> application/json, TOML body -> application/toml).
Avoid vendor or suffixed MIME types (application/vnd.*+json); Quickwit matches only the plain subtype.
Add a preflight validation in CI scripts or SDK wrappers that whitelists content types for Quickwit config endpoints.
When a 415 comes back, immediately inspect the Content-Type header before debugging the body.

When it happens

Trigger: Sending POST/PUT to /indexes, /indexes/{index}/sources, or index-template endpoints with a `Content-Type` such as `application/xml`, `text/plain`, `application/x-www-form-urlencoded`, or a vendor type whose subtype Quickwit does not map (e.g. `application/hal+json` resolves to subtype `hal+json`, not `json`).

Common situations: curl or HTTP client defaulting to no/incorrect Content-Type; REST client tools posting form data; SDK-generated clients sending vendor MIME types like `application/vnd.api+json`; copy-pasted requests where the body is JSON but the header says `text/plain`.

Related errors

AI-assisted analysis of quickwit-oss/quickwit@a39730c5cd (2026-09-08). Data as JSON: /api/errors/b93c70e4040a8a80. Report an issue: GitHub.

Appendix: source

Thrown at quickwit/quickwit-serve/src/format.rs:105

#[error(
    "request's content-type is not supported: supported media types are `application/json`, \
     `application/toml`, and `application/yaml`"
)]
pub(crate) struct UnsupportedMediaType;

impl warp::reject::Reject for UnsupportedMediaType {}

pub(crate) fn extract_config_format()
-> impl Filter<Extract = (ConfigFormat,), Error = Rejection> + Copy {
    warp::filters::header::optional::<mime_guess::Mime>(CONTENT_TYPE.as_str()).and_then(
        |mime_opt: Option<mime_guess::Mime>| {
            if let Some(mime) = mime_opt {
                let config_format = match mime.subtype().as_str() {
                    "json" => ConfigFormat::Json,
                    "toml" => ConfigFormat::Toml,
                    "yaml" => ConfigFormat::Yaml,
                    _ => {
                        return futures::future::err(warp::reject::custom(UnsupportedMediaType));
                    }
                };
                return futures::future::ok(config_format);
            }
            futures::future::ok(ConfigFormat::Json)
        },
    )
}

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