BoundaryML/baml · error

BAML internal error (AWSBedrock): file should have been reso

Error message

BAML internal error (AWSBedrock): file should have been resolved to base64

What it means

When building a Bedrock message containing an Image, BAML expects every BamlMedia with BamlMediaContent::File to have been converted to base64/url data in an earlier resolution pass. If a raw File variant survives into to_media_message, this internal invariant is broken and BAML bails. It signals a bug in BAML's media resolution pipeline rather than a user input the AWS API rejected.

Source

Thrown at engine/baml-runtime/src/internal/llm_client/primitive/aws/aws_client.rs:1154

    fn to_media_message(
        &self,
        media: &baml_types::BamlMedia,
    ) -> Result<bedrock::types::ContentBlock> {
        match media.media_type {
            BamlMediaType::Image => {
                let format = bedrock::types::ImageFormat::from(
                    {
                        let mime_type = media.mime_type_as_ok()?;
                        match mime_type.strip_prefix("image/") {
                            Some(s) => s.to_string(),
                            None => mime_type,
                        }
                    }
                    .as_str(),
                );
                match &media.content {
                    BamlMediaContent::File(_) => {
                        anyhow::bail!(
                            "BAML internal error (AWSBedrock): file should have been resolved to base64"
                        )
                    }
                    BamlMediaContent::Url(url) => Ok(bedrock::types::ContentBlock::Image(
                        bedrock::types::ImageBlock::builder()
                            .set_format(Some(format))
                            .set_source(Some(bedrock::types::ImageSource::S3Location(
                                bedrock::types::S3Location::builder()
                                    .set_uri(Some(url.url.clone()))
                                    .build()
                                    .context("Failed to build S3Location block")?,
                            )))
                            .build()
                            .context("Failed to build Image block")?,
                    )),
                    BamlMediaContent::Base64(b64_media) => Ok(bedrock::types::ContentBlock::Image(
                        bedrock::types::ImageBlock::builder()
                            .set_format(Some(format))

View on GitHub (pinned to bd85ce9dee)

Solutions

1. Upgrade BAML to the latest version — this is an internal invariant failure, likely already fixed.
2. Pass the image as base64 data or a URL instead of a raw file path reference.
3. Explicitly set media_type/mime so the resolver recognizes and resolves the file.
4. File a bug report with the baml-lang/baml repo including the media input that triggered it.

Example fix

// before
image baml_image({ url: "file://./cat.png" })
// after — ensure file resolves, or inline base64
image baml_image({ url: "data:image/png;base64,<base64-data>" })

// Ensure media is resolved before sending to Bedrock
if (media.url && media.url.startsWith("file://")) {
  media.url = "data:image/png;base64," + fs.readFileSync(stripFileScheme(media.url)).toString("base64");
}

const isResolved = (m) => typeof m.url === 'string' && (m.url.startsWith('data:') || m.url.startsWith('http'));

try { await bamlClient.MyPrompt(...) } catch (e) { if (String(e.message).includes('should have been resolved to base64')) { /* upgrade BAML / inline base64 and retry */ } else throw e; }

When it happens

Trigger: Calling an AWS Bedrock client with an image media argument whose content is still a file path reference (BamlMediaContent::File) at request-build time — i.e. the media resolver failed to inline the file as base64 before to_media_message runs.

Common situations: Hitting a BAML runtime bug in a version where a file:// or relative-path image was not resolved (e.g. unusual file paths, missing file resolution for certain providers), or constructing media programmatically via internal APIs without running resolution.

Understand the failure class

Background: "This is a bug, please report it": internal invariant violations, unreachable panics, and SNH errors explained — this error's family across 47 libraries.

Related errors

• BAML internal error (AWSBedrock): Pdf file should have been
• BAML internal error (AWSBedrock): video file should have bee
• BAML internal error (google-ai): file should have been resol
• BAML internal error (Vertex): file should have been resolved
• VM internal error: {0}

AI-assisted analysis of BoundaryML/baml@bd85ce9dee (2026-09-12). Data as JSON: /api/errors/72e4cde3a9e68902. Report an issue: GitHub.