xai-org/grok-build · error

Invalid ACP content blocks in "content": {e}

Error message

Invalid ACP content blocks in "content": {e}

What it means

For the {"type":"acp","content":[...]} wrapper form, the "content" value is deserialized into Vec<acp::ContentBlock> via serde_json::from_value. If the content array's elements violate the ContentBlock schema, the serde error is wrapped as "Invalid ACP content blocks in \"content\": {e}". This localizes the failure to the content field specifically.

Source

Thrown at crates/codegen/xai-grok-pager/src/headless/cli.rs:114

    let blocks: Vec<acp::ContentBlock> = match value {
        serde_json::Value::Array(_) => serde_json::from_value(value)
            .map_err(|e| anyhow::anyhow!("Invalid ACP content blocks: {e}"))?,

        serde_json::Value::Object(ref map) => {
            let format_type = map.get("type").and_then(|v| v.as_str()).ok_or_else(|| {
                anyhow::anyhow!(
                    "JSON object must have a \"type\" field \
                         (e.g., {{\"type\": \"acp\", \"content\": [...]}})"
                )
            })?;
            let content = map
                .get("content")
                .ok_or_else(|| anyhow::anyhow!("JSON object must have a \"content\" field"))?;

            match format_type {
                "acp" => serde_json::from_value(content.clone()).map_err(|e| {
                    anyhow::anyhow!("Invalid ACP content blocks in \"content\": {e}")
                })?,
                other => anyhow::bail!(
                    "Unsupported prompt format type: \"{other}\". Supported types: \"acp\""
                ),
            }
        }

        _ => {
            anyhow::bail!("Expected JSON array or {{\"type\": \"...\", \"content\": [...]}} object")
        }
    };

    if blocks.is_empty() {
        anyhow::bail!("content blocks array is empty");
    }
    Ok(blocks)
}

View on GitHub (pinned to bc7f02eddd)

Solutions

  1. Read the serde detail for the failing index/field and fix that block.
  2. Ensure "content" is an array, wrapping a single block in [ ... ].
  3. Match each block exactly to acp::ContentBlock variants (valid "type" plus required fields).
  4. Generate the payload with serde_json::json! or from a known-good example to guarantee the schema.

Example fix

// before
{"type":"acp","content":{"type":"text","text":"hi"}}
// after
{"type":"acp","content":[{"type":"text","text":"hi"}]}
Defensive patterns

Strategy: validation

Validate before calling

fn content_blocks_ok(s: &str) -> bool {
    serde_json::from_str::<serde_json::Value>(s)
        .ok()
        .and_then(|v| v.get("content").cloned())
        .map(|c| serde_json::from_value::<Vec<xai_grok_shell::acp::ContentBlock>>(c).is_ok())
        .unwrap_or(false)
}

Type guard

fn is_block_array(v: &serde_json::Value) -> bool {
    v.as_array()
        .map(|a| !a.is_empty() || true)
        .unwrap_or(false)
}
// array-ness is cheap; full schema check requires from_value::<Vec<acp::ContentBlock>>

Try / catch

match HeadlessPrompt::from_json(&raw) {
    Ok(p) => p,
    Err(e) if e.to_string().contains("Invalid ACP content blocks in \"content\"") => {
        eprintln!("fix the block at the index serde reports: {e}");
        std::process::exit(2);
    }
    Err(e) => return Err(e),
}

Prevention

When it happens

Trigger: Wrapper object has type:"acp" and a "content" key, but the content value is not an array of valid ContentBlocks: unknown block "type", missing required fields, wrong field types, or content being a single object/string instead of an array.

Common situations: Putting one block object directly in "content" instead of an array; using block types from a different ACP version; nested image/tool blocks with mismatched field names.

Understand the failure class

Background: Schema validation failed / invalid input schema: payload rejected because its shape doesn't match the expected schema — this error's family across 28 libraries.

Related errors

AI-assisted analysis of xai-org/grok-build@bc7f02eddd (2026-08-31). Data as JSON: /api/errors/8152b0393803d99b. Report an issue: GitHub.