What causes "Invalid HTTP library " + getLibrary() + ". Only httr, httr2 are supported." in OpenAPITools/openapi-generator?

Use -l httr or -l httr2 (exact lowercase)

OpenAPITools/openapi-generator · error · IllegalArgumentException

Invalid HTTP library " + getLibrary() + ". Only httr, httr2

Error message

Invalid HTTP library " + getLibrary() + ". Only httr, httr2 are supported.

What it means

The R client generator supports exactly two HTTP libraries: httr and httr2. In processOpts() the library value selects template branches (httr2 additionally enables the generateWrapper option and the *_api.R wrapper); any other -l/--library value falls into the else branch and throws IllegalArgumentException listing the supported values.

Source

Thrown at modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/RClientCodegen.java:348

        supportingFiles.add(new SupportingFile("ApiResponse.mustache", File.separator + "R", "api_response.R"));
        supportingFiles.add(new SupportingFile("api_client.mustache", File.separator + "R", "api_client.R"));
        supportingFiles.add(new SupportingFile("NAMESPACE.mustache", "", "NAMESPACE"));
        supportingFiles.add(new SupportingFile("testthat.mustache", File.separator + "tests", "testthat.R"));
        supportingFiles.add(new SupportingFile("r-client.mustache", File.separator + ".github" + File.separator + "workflows", "r-client.yaml"));
        supportingFiles.add(new SupportingFile("lintr.mustache", "", ".lintr"));

        if (HTTR.equals(getLibrary())) {
            // for httr
            setLibrary(HTTR);
        } else if (HTTR2.equals(getLibrary())) {
            // for httr2
            setLibrary(HTTR2);
            additionalProperties.put("isHttr2", Boolean.TRUE);
            if (generateWrapper) { // generateWrapper option only supports in httr2 library
                supportingFiles.add(new SupportingFile("api_wrapper.mustache", "R", packageName.toLowerCase(Locale.ROOT) + "_api.R"));
            }
        } else {
            throw new IllegalArgumentException("Invalid HTTP library " + getLibrary() + ". Only httr, httr2 are supported.");
        }

        // add lambda for mustache templates to fix license field
        additionalProperties.put("lambdaLicense", new Mustache.Lambda() {
            @Override
            public void execute(Template.Fragment fragment, Writer writer) throws IOException {
                String content = fragment.execute();
                content = content.trim().replace("Apache-2.0", "Apache License 2.0");
                writer.write(content);
            }
        });

        // add lambda for mustache templates to escape %
        additionalProperties.put("lambdaRdocEscape", new Mustache.Lambda() {
            @Override
            public void execute(Template.Fragment fragment, Writer writer) throws IOException {
                String content = fragment.execute();
                content = content.trim().replace("%", "\\%");

View on GitHub (pinned to fcec517be3)

Solutions

Use -l httr or -l httr2 (exact lowercase)
Omit -l entirely to take the generator default instead of guessing a value
If you need the wrapper API, use -l httr2 together with -c generateWrapper=true (wrapper is httr2-only)

Example fix

# before
openapi-generator-cli generate -i api.yaml -g r -l httr3
# after
openapi-generator-cli generate -i api.yaml -g r -l httr2 -c generateWrapper=true

Defensive patterns

Strategy: validation

Validate before calling

# bash: whitelist the library before generating
R_LIBS='httr httr2'
[[ " ${R_LIBS} " == *" ${R_LIBRARY:-httr} "* ]] || { echo "-l must be one of: ${R_LIBS}"; exit 1; }
openapi-generator-cli generate -i api.yaml -g r -l "${R_LIBRARY:-httr}"

Try / catch

try {
    RClientCodegen codegen = new RClientCodegen();
    codegen.setLibrary("httr2"); // or leave default
    new DefaultGenerator().opts(new ClientOptInput().opts(codegen)).generate();
} catch (IllegalArgumentException e) {
    // 'Invalid HTTP library ...' - only httr and httr2 are valid; fix and rerun
}

Prevention

Pin -l httr or -l httr2 explicitly in CI instead of templating from other generators
Remember generateWrapper only works with httr2
Omit -l to fall back to the generator default when unsure

When it happens

Trigger: openapi-generator-cli generate -i api.yaml -g r -l curl / -l httr3 / -l restifts; also setting <library> in the Maven plugin to a value copied from another generator's docs.

Common situations: Copy-pasting a -l flag from a python or java example into an R job; assuming the library flag is free-form; typos like httr2-client. The flag is also case-sensitive: HTTR vs httr are compared exactly.

Related errors

AI-assisted analysis of OpenAPITools/openapi-generator@fcec517be3 (2026-08-22). Data as JSON: /api/errors/eb7cb6290557bdd2. Report an issue: GitHub.