hashicorp/packer · error

failed to write file %q as base64: %s

Error message

failed to write file %q as base64: %s

What it means

The `filebase64()` HCL2 function read the file successfully but the base64 encoder failed while writing the content to its output builder. Like the gzip writes, this targets a strings.Builder and is effectively unreachable defensive code — a strings.Builder Write never returns an error.

Source

Thrown at hcl2template/function/filebase64.go:37

			Name:        "path",
			Description: "Read a file and encode it as a base64 string",
			Type:        cty.String,
		},
	},
	Type:         function.StaticReturnType(cty.String),
	RefineResult: refineNotNull,
	Impl: func(args []cty.Value, retType cty.Type) (cty.Value, error) {
		path := args[0].AsString()
		content, err := os.ReadFile(path)
		if err != nil {
			return cty.NullVal(cty.String), fmt.Errorf("failed to read file %q: %s", path, err)
		}

		out := &strings.Builder{}
		enc := base64.NewEncoder(base64.StdEncoding, out)
		_, err = enc.Write(content)
		if err != nil {
			return cty.NullVal(cty.String), fmt.Errorf("failed to write file %q as base64: %s", path, err)
		}
		_ = enc.Close()

		return cty.StringVal(out.String()), nil
	},
})

View on GitHub (pinned to eb36e3c3e4)

Solutions

1. Re-run the packer command
2. If reproducible, report to Packer — the error path should be unreachable
3. Check available memory if encoding a very large file

// unreachable in practice; retry the command
packer build template.pkr.hcl || retry=1

When it happens

Trigger: Calling `filebase64(path)` where the internal base64.Encoder.Write returns an error — practically never since it wraps a strings.Builder.

Common situations: Not observed in real usage; exists for complete encoder error handling.

Related errors

• failed to read file %q: %s
• too many values, 1 needed: %v
• failed to write gzip raw data: %w
• failed to flush gzip writer: %w
• failed to close gzip writer: %w

AI-assisted analysis of hashicorp/packer@eb36e3c3e4 (2026-09-05). Data as JSON: /api/errors/a1fa1cf185342798. Report an issue: GitHub.