[propagator-xray] X-Amzn-Trace-Id inject key is mixed-case, breaking gRPC metadata usage

[gonsuke]

Description of the bug

When OpenTelemetry::Propagator::XRay::TextMapPropagator is used as a propagator and OpenTelemetry.propagation.inject(metadata) is called with a gRPC metadata hash, the key X-Amzn-Trace-Id (mixed-case) is injected. However, gRPC requires metadata keys to match [a-z0-9-_.] (lowercase only), this causes a runtime error.

The relevant line in text_map_propagator.rb

XRAY_CONTEXT_KEY = 'X-Amzn-Trace-Id'  # line 20
# ...
setter.set(carrier, XRAY_CONTEXT_KEY, xray_value)  # line 98

Share details about your runtime

• Operating system details: Linux Debian bookworm, macOS 26.3.1
• Ruby 3.4.4
• opentelemetry-propagator-xray: 0.26.1
• opentelemetry-sdk: 1.10.0
• grpc gem (Ruby gRPC)

Share a simplified reproduction if possible

require 'opentelemetry/sdk'
require 'opentelemetry-propagator-xray'
require 'grpc'

OpenTelemetry::SDK.configure do |c|
  c.propagators = [
    OpenTelemetry::Trace::Propagation::TraceContext.text_map_propagator,
    OpenTelemetry::Propagator::XRay::TextMapPropagator.new
  ]
  c.service_name = 'repro'
end

metadata = {}
tracer = OpenTelemetry.tracer_provider.tracer('repro')
tracer.in_span('test') do
  OpenTelemetry.propagation.inject(metadata)
end

puts "Injected keys : #{metadata.keys.inspect}"

begin
  chan = GRPC::Core::Channel.new('localhost:9999', nil, :this_channel_is_insecure)
  call = chan.create_call(nil, nil, '/blah/method', nil, Time.now + 1)
  call.run_batch(GRPC::Core::CallOps::SEND_INITIAL_METADATA => metadata)
rescue GRPC::BadStatus, GRPC::Core::CallError => e
  puts "gRPC error     : #{e.class}: #{e.message}"
rescue StandardError => e
  puts "Other error    : #{e.class}: #{e.message}"
end

Output:

Injected keys : ["traceparent", "X-Amzn-Trace-Id"]
Other error    : ArgumentError: 'X-Amzn-Trace-Id' is an invalid header key, must match [a-z0-9-_.]+

Workaround

I worked around this by wrapping the gRPC metadata hash in a carrier that normalizes keys to lowercase before writing:

class LowercaseCarrier
  def initialize(hash) = @hash = hash
  def []=(key, value)  = @hash[key.downcase] = value
  def [](key)          = @hash[key.downcase]
  def keys             = @hash.keys
end

OpenTelemetry.propagation.inject(LowercaseCarrier.new(metadata))

The AWS X-Ray header name is case-insensitive at the HTTP level (per RFC 7230), so I'd imagine lowercase would be fine... but I wanted to double check here before assuming anything.

Thanks for maintaining these gems. It's been a solid building block for our tracing setup on AWS.

_{Tip: React with 👍 to help prioritize this issue. Please use comments to provide useful context, avoiding +1 or me too, to help us triage it. Learn more in our end user docs.}