deepseek-ai/deepseek-harness · error

the image data is not canonical base64

Error message

the image data is not canonical base64

What it means

Error "the image data is not canonical base64" thrown in deepseek-ai/deepseek-harness.

Source

Thrown at packages/mcp/mcp-client/src/tools.ts:384

}

/** Narrow one JSON value to a string-keyed object. */
function isRecord(value: JsonValue): value is { [key: string]: JsonValue } {
  return typeof value === 'object' && value !== null && !Array.isArray(value)
}

/** Narrow a declared MIME string to the durable image vocabulary. */
function isImageMediaType(value: string): value is ImageMediaType {
  return IMAGE_MEDIA_TYPES.includes(value as ImageMediaType)
}

/** Decode one untrusted MCP image block without accepting base64 aliases. */
function decodeImage(block: McpContentBlock): SaveImageAttachment {
  if (block.mimeType === undefined || !isImageMediaType(block.mimeType)) {
    throw new Error('the declared media type is not PNG, JPEG, WebP, or GIF')
  }
  if (block.data === undefined || !CANONICAL_BASE64.test(block.data)) {
    throw new Error('the image data is not canonical base64')
  }
  const data = Buffer.from(block.data, 'base64')
  if (data.toString('base64') !== block.data) {
    throw new Error('the image data is not canonical base64')
  }
  return { data, mediaType: block.mimeType }
}

/**
 * Resolve the active model route and durable store for an image-bearing result.
 * @param ctx - plugin context with optional services.
 * @param exec - exact tool execution whose agent supplies the latest route.
 * @returns the attachment store after exact positive image-capability proof.
 */
async function resolveImageAdmission(ctx: Context, exec: ToolExecution): Promise<AttachmentStore> {
  const attachments = ctx.get('attachments')
  if (attachments === undefined) throw new Error('no attachment store is mounted')
  const routed = exec.agent?.session.requestHeader()?.config

View on GitHub (pinned to b150a551b8)

Solutions

1. Re-encode the image data as canonical base64.

When it happens

Trigger: Thrown at packages/mcp/mcp-client/src/tools.ts:384 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of deepseek-ai/deepseek-harness@b150a551b8 (2026-08-24). Data as JSON: /api/errors/e78fe1e0d799104b. Report an issue: GitHub.