aws_functions.h

/* AWS V4 Signature implementation
 *
 * This file contains the modularized source code for accepting a given HTTP
 * request as ngx_http_request_t and modifiying it to introduce the
 * Authorization header in compliance with the AWS V4 spec. The IAM access
 * key and the signing key (not to be confused with the secret key) along
 * with it's scope are taken as inputs.
 *
 * The actual nginx module binding code is not present in this file. This file
 * is meant to serve as an "AWS Signing SDK for nginx".
 *
 * Maintainer/contributor rules
 *
 * (1) All functions here need to be static and inline.
 * (2) Every function must have it's own set of unit tests.
 * (3) The code must be written in a thread-safe manner. This is usually not
 *     a problem with standard nginx functions. However, care must be taken
 *     when using very old C functions such as strtok, gmtime, etc. etc.
 *     Always use the _r variants of such functions
 * (4) All heap allocation must be done using ngx_pool_t instead of malloc
 */

#ifndef __NGX_AWS_FUNCTIONS_INTERNAL__H__
#define __NGX_AWS_FUNCTIONS_INTERNAL__H__

#include <time.h>
#include <ngx_times.h>
#include <ngx_core.h>
#include <ngx_http.h>

#include "crypto_helper.h"

#define AMZ_DATE_MAX_LEN 20
#define STRING_TO_SIGN_LENGTH 3000

typedef ngx_keyval_t header_pair_t;

struct AwsCanonicalRequestDetails {
	ngx_str_t *canon_request;
	ngx_str_t *signed_header_names;
	ngx_array_t *header_list; // list of header_pair_t
};

struct AwsCanonicalHeaderDetails {
	ngx_str_t *canon_header_str;
	ngx_str_t *signed_header_names;
	ngx_array_t *header_list; // list of header_pair_t
};

struct AwsSignedRequestDetails {
	const ngx_str_t *signature;
	const ngx_str_t *signed_header_names;
	ngx_array_t *header_list; // list of header_pair_t
};

// mainly useful to avoid having to full instantiate request structures for
// tests...
#define safe_ngx_log_error(req, ...)                                  \
  if (req->connection) {                                              \
    ngx_log_error(NGX_LOG_ERR, req->connection->log, 0, __VA_ARGS__); \
  }

static const ngx_str_t EMPTY_STRING_SHA256 = ngx_string("e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855");
static const ngx_str_t EMPTY_STRING = ngx_null_string;
static const ngx_str_t AMZ_HASH_HEADER = ngx_string("x-amz-content-sha256");
static const ngx_str_t AMZ_DATE_HEADER = ngx_string("x-amz-date");
static const ngx_str_t AMZ_SECURITY_TOKEN_HEADER = ngx_string("x-amz-security-token");
static const ngx_str_t HOST_HEADER = ngx_string("host");
static const ngx_str_t AUTHZ_HEADER = ngx_string("authorization");

static inline char* __CHAR_PTR_U(u_char* ptr) {return (char*)ptr;}
static inline const char* __CONST_CHAR_PTR_U(const u_char* ptr) {return (const char*)ptr;}

static inline const ngx_str_t* ngx_aws_auth__compute_request_time(ngx_pool_t *pool, const time_t *timep) {
	ngx_str_t *const retval = ngx_palloc(pool, sizeof(ngx_str_t));
	retval->data = ngx_palloc(pool, AMZ_DATE_MAX_LEN);
	struct tm *tm_p = ngx_palloc(pool, sizeof(struct tm));
	gmtime_r(timep, tm_p);
	retval->len = strftime(__CHAR_PTR_U(retval->data), AMZ_DATE_MAX_LEN - 1, "%Y%m%dT%H%M%SZ", tm_p);
	return retval;
}

static inline int ngx_aws_auth__cmp_hnames(const void *one, const void *two) {
    header_pair_t *first, *second;
    int ret;
    first  = (header_pair_t *) one;
    second = (header_pair_t *) two;
    ret = ngx_strncmp(first->key.data, second->key.data, ngx_min(first->key.len, second->key.len));
    if (ret != 0){
        return ret;
    } else {
        return (first->key.len - second->key.len);
    }
}

static inline const ngx_str_t* ngx_aws_auth__canonize_query_string(ngx_pool_t *pool,
	const ngx_http_request_t *req) {
	u_char *p, *ampersand, *equal, *last;
	size_t i, len;
	ngx_str_t *retval = ngx_palloc(pool, sizeof(ngx_str_t));

	header_pair_t *qs_arg;
	ngx_array_t *query_string_args = ngx_array_create(pool, 0, sizeof(header_pair_t));

	if (req->args.len == 0) {
		return &EMPTY_STRING;
	}

	p = req->args.data;
	last = p + req->args.len;

	for ( /* void */ ; p < last; p++) {
		qs_arg = ngx_array_push(query_string_args);

		ampersand = ngx_strlchr(p, last, '&');
		if (ampersand == NULL) {
			ampersand = last;
		}

		equal = ngx_strlchr(p, last, '=');
		if ((equal == NULL) || (equal > ampersand)) {
			equal = ampersand;
		}

		len = equal - p;
		qs_arg->key.data = ngx_palloc(pool, len*3);
		qs_arg->key.len = (u_char *)ngx_escape_uri(qs_arg->key.data, p, len, NGX_ESCAPE_ARGS) - qs_arg->key.data;


		len = ampersand - equal;
		if(len > 0 ) {
			qs_arg->value.data = ngx_palloc(pool, len*3);
			qs_arg->value.len = (u_char *)ngx_escape_uri(qs_arg->value.data, equal+1, len-1, NGX_ESCAPE_ARGS) - qs_arg->value.data;
		} else {
			qs_arg->value = EMPTY_STRING;
		}

		p = ampersand;
	}

	ngx_qsort(query_string_args->elts, (size_t) query_string_args->nelts,
		sizeof(header_pair_t), ngx_aws_auth__cmp_hnames);

	retval->data = ngx_palloc(pool, req->args.len*3 + query_string_args->nelts*2);
	retval->len = 0;

	for(i = 0; i < query_string_args->nelts; i++) {
		qs_arg = &((header_pair_t*)query_string_args->elts)[i];

		ngx_memcpy(retval->data + retval->len, qs_arg->key.data, qs_arg->key.len);
		retval->len += qs_arg->key.len;

		*(retval->data + retval->len) = '=';
		retval->len++;

		ngx_memcpy(retval->data + retval->len, qs_arg->value.data, qs_arg->value.len);
		retval->len += qs_arg->value.len;

		*(retval->data + retval->len) = '&';
		retval->len++;
	}
	retval->len--;

  safe_ngx_log_error(req, "canonical qs constructed is %V", retval);

	return retval;
}


static inline const ngx_str_t* ngx_aws_auth__host_from_bucket(ngx_pool_t *pool,
		const ngx_str_t *s3_bucket) {
	static const char HOST_PATTERN[] = ".s3.amazonaws.com";
	ngx_str_t *host;

	host = ngx_palloc(pool, sizeof(ngx_str_t));
	host->len = s3_bucket->len + sizeof(HOST_PATTERN) + 1;
	host->data = ngx_palloc(pool, host->len);
	host->len = ngx_snprintf(host->data, host->len, "%V%s", s3_bucket, HOST_PATTERN) - host->data;

	return host;
}

static inline struct AwsCanonicalHeaderDetails ngx_aws_auth__canonize_headers(ngx_pool_t *pool,
		const ngx_http_request_t *req,
		const ngx_str_t *s3_bucket, const ngx_str_t *amz_date,
		const ngx_str_t *content_hash,
    	const ngx_str_t *s3_endpoint,
		const ngx_str_t *security_token) {
	size_t header_names_size = 1, header_nameval_size = 1;
	size_t i, used;
	u_char *buf_progress;
	struct AwsCanonicalHeaderDetails retval;

	ngx_array_t *settable_header_array = ngx_array_create(pool, 4, sizeof(header_pair_t));
	header_pair_t *header_ptr;

	header_ptr = ngx_array_push(settable_header_array);
	header_ptr->key = AMZ_HASH_HEADER;
	header_ptr->value = *content_hash;

	header_ptr = ngx_array_push(settable_header_array);
	header_ptr->key = AMZ_DATE_HEADER;
	header_ptr->value = *amz_date;

	if (ngx_strncmp(security_token, &EMPTY_STRING, 1) != 0) {
		header_ptr = ngx_array_push(settable_header_array);
		header_ptr->key = AMZ_SECURITY_TOKEN_HEADER;
		header_ptr->value = *security_token;
	}

	header_ptr = ngx_array_push(settable_header_array);
	header_ptr->key = HOST_HEADER;
	header_ptr->value.len = s3_bucket->len + 60;
	header_ptr->value.data = ngx_palloc(pool, header_ptr->value.len);
	header_ptr->value.len = ngx_snprintf(header_ptr->value.data, header_ptr->value.len, "%V.%V", s3_bucket, s3_endpoint) - header_ptr->value.data;

	ngx_qsort(settable_header_array->elts, (size_t) settable_header_array->nelts,
		sizeof(header_pair_t), ngx_aws_auth__cmp_hnames);
	retval.header_list = settable_header_array;

	for(i = 0; i < settable_header_array->nelts; i++) {
		header_names_size += ((header_pair_t*)settable_header_array->elts)[i].key.len + 1;
		header_nameval_size += ((header_pair_t*)settable_header_array->elts)[i].key.len + 1;
		header_nameval_size += ((header_pair_t*)settable_header_array->elts)[i].value.len + 2;
	}

	/* make canonical headers string */
	retval.canon_header_str = ngx_palloc(pool, sizeof(ngx_str_t));
	retval.canon_header_str->data = ngx_palloc(pool, header_nameval_size);

	for(i = 0, used = 0, buf_progress = retval.canon_header_str->data;
		i < settable_header_array->nelts;
		i++, used = buf_progress - retval.canon_header_str->data) {
		buf_progress = ngx_snprintf(buf_progress, header_nameval_size - used, "%V:%V\n",
			& ((header_pair_t*)settable_header_array->elts)[i].key,
			& ((header_pair_t*)settable_header_array->elts)[i].value);
	}
	retval.canon_header_str->len = used;

	/* make signed headers */
	retval.signed_header_names = ngx_palloc(pool, sizeof(ngx_str_t));
	retval.signed_header_names->data = ngx_palloc(pool, header_names_size);

	for(i = 0, used = 0, buf_progress = retval.signed_header_names->data;
		i < settable_header_array->nelts;
		i++, used = buf_progress - retval.signed_header_names->data) {
		buf_progress = ngx_snprintf(buf_progress, header_names_size - used, "%V;",
			& ((header_pair_t*)settable_header_array->elts)[i].key);
	}
	used--;
	retval.signed_header_names->len = used;
	retval.signed_header_names->data[used] = 0;

	return retval;
}

static inline const ngx_str_t* ngx_aws_auth__request_body_hash(ngx_pool_t *pool,
	const ngx_http_request_t *req) {
	/* TODO: support cases involving non-empty body */
	return &EMPTY_STRING_SHA256;
}

// AWS wants a peculiar kind of URI-encoding: they want RFC 3986, except that
// slashes shouldn't be encoded...
// this function is a light wrapper around ngx_escape_uri that does exactly that
// modifies the source in place if it needs to be escaped
// see http://docs.aws.amazon.com/general/latest/gr/sigv4-create-canonical-request.html
static inline void ngx_aws_auth__escape_uri(ngx_pool_t *pool, ngx_str_t* src) {
  u_char *escaped_data;
  u_int escaped_data_len, escaped_data_with_slashes_len, i, j;
  uintptr_t escaped_count, slashes_count = 0;

  // first, we need to know how many characters need to be escaped
  escaped_count = ngx_escape_uri(NULL, src->data, src->len, NGX_ESCAPE_URI_COMPONENT);
  // except slashes should not be escaped...
  if (escaped_count > 0) {
    for (i = 0; i < src->len; i++) {
      if (src->data[i] == '/') {
        slashes_count++;
      }
    }
  }

  if (escaped_count == slashes_count) {
    // nothing to do! nothing but slashes escaped (if even that)
    return;
  }

  // each escaped character is replaced by 3 characters
  escaped_data_len = src->len + escaped_count * 2;
  escaped_data = ngx_palloc(pool, escaped_data_len);
  ngx_escape_uri(escaped_data, src->data, src->len, NGX_ESCAPE_URI_COMPONENT);

  // now we need to go back and re-replace each occurrence of %2F with a slash
  escaped_data_with_slashes_len = src->len + (escaped_count - slashes_count) * 2;
  if (slashes_count > 0) {
    for (i = 0, j = 0; i < escaped_data_with_slashes_len; i++) {
      if (j < escaped_data_len - 2 && strncmp((char*) (escaped_data + j), "%2F", 3) == 0) {
        escaped_data[i] = '/';
        j += 3;
      } else {
        escaped_data[i] = escaped_data[j];
        j++;
      }
    }

    src->len = escaped_data_with_slashes_len;
  } else {
    // no slashes
    src->len = escaped_data_len;
  }

  src->data = escaped_data;
}

static inline const ngx_str_t* ngx_aws_auth__canon_url(ngx_pool_t *pool, const ngx_http_request_t *req) {
	ngx_str_t *retval;
  const u_char *req_uri_data;
  u_int req_uri_len;

  if(req->args.len == 0) {
    req_uri_data = req->uri.data;
    req_uri_len = req->uri.len;
  } else {
    req_uri_data = req->uri_start;
    req_uri_len = req->args_start - req->uri_start - 1;
  }

  // we need to copy that data to not modify the request for other modules
  retval = ngx_palloc(pool, sizeof(ngx_str_t));
  retval->data = ngx_palloc(pool, req_uri_len);
  ngx_memcpy(retval->data, req_uri_data, req_uri_len);
  retval->len = req_uri_len;

  safe_ngx_log_error(req, "canonical url extracted before URI encoding is %V", retval);

  // then URI-encode it per RFC 3986
  ngx_aws_auth__escape_uri(pool, retval);
  safe_ngx_log_error(req, "canonical url extracted after URI encoding is %V", retval);

  return retval;
}

static inline struct AwsCanonicalRequestDetails ngx_aws_auth__make_canonical_request(ngx_pool_t *pool,
		const ngx_http_request_t *req,
		const ngx_str_t *s3_bucket_name, const ngx_str_t *amz_date,
		const ngx_str_t *s3_endpoint, const ngx_str_t *security_token) {
	struct AwsCanonicalRequestDetails retval;

	// canonize query string
	const ngx_str_t *canon_qs = ngx_aws_auth__canonize_query_string(pool, req);

	// compute request body hash
	const ngx_str_t *request_body_hash = ngx_aws_auth__request_body_hash(pool, req);

	const struct AwsCanonicalHeaderDetails canon_headers =
		ngx_aws_auth__canonize_headers(pool, req, s3_bucket_name, amz_date, request_body_hash, s3_endpoint, security_token);
	retval.signed_header_names = canon_headers.signed_header_names;

	const ngx_str_t *http_method = &(req->method_name);
	const ngx_str_t *url = ngx_aws_auth__canon_url(pool, req);

	retval.canon_request = ngx_palloc(pool, sizeof(ngx_str_t));
	retval.canon_request->len = 10000;
	retval.canon_request->data = ngx_palloc(pool, retval.canon_request->len);

	retval.canon_request->len = ngx_snprintf(retval.canon_request->data, retval.canon_request->len, "%V\n%V\n%V\n%V\n%V\n%V",
		http_method, url, canon_qs, canon_headers.canon_header_str,
		canon_headers.signed_header_names, request_body_hash) - retval.canon_request->data;
	retval.header_list = canon_headers.header_list;

  safe_ngx_log_error(req, "canonical req is %V", retval.canon_request);

	return retval;
}

static inline const ngx_str_t* ngx_aws_auth__string_to_sign(ngx_pool_t *pool,
		const ngx_str_t *key_scope,	const ngx_str_t *date, const ngx_str_t *canon_request_hash) {
	ngx_str_t *retval = ngx_palloc(pool, sizeof(ngx_str_t));

	retval->len = STRING_TO_SIGN_LENGTH;
	retval->data = ngx_palloc(pool, retval->len);
	retval->len = ngx_snprintf(retval->data, retval->len, "AWS4-HMAC-SHA256\n%V\n%V\n%V",
		date, key_scope, canon_request_hash) - retval->data ;

	return retval;
}

static inline const ngx_str_t* ngx_aws_auth__make_auth_token(ngx_pool_t *pool,
	const ngx_str_t *signature, const ngx_str_t *signed_header_names,
	const ngx_str_t *access_key_id, const ngx_str_t *key_scope) {

    const char FMT_STRING[] = "AWS4-HMAC-SHA256 Credential=%V/%V,SignedHeaders=%V,Signature=%V";
	ngx_str_t *authz;

	authz = ngx_palloc(pool, sizeof(ngx_str_t));
	authz->len = access_key_id->len + key_scope->len + signed_header_names->len
		+ signature->len + sizeof(FMT_STRING);
	authz->data = ngx_palloc(pool, authz->len);
    authz->len = ngx_snprintf(authz->data, authz->len, FMT_STRING,
		access_key_id, key_scope, signed_header_names, signature) - authz->data;
	return authz;
}

static inline struct AwsSignedRequestDetails ngx_aws_auth__compute_signature(ngx_pool_t *pool, ngx_http_request_t *req,
		const ngx_str_t *signing_key,
		const ngx_str_t *key_scope,
		const ngx_str_t *s3_bucket_name,
    	const ngx_str_t *s3_endpoint,
		const ngx_str_t *security_token) {
	struct AwsSignedRequestDetails retval;

	const ngx_str_t *date = ngx_aws_auth__compute_request_time(pool, &req->start_sec);
	const struct AwsCanonicalRequestDetails canon_request =
		ngx_aws_auth__make_canonical_request(pool, req, s3_bucket_name, date, s3_endpoint, security_token);
	const ngx_str_t *canon_request_hash = ngx_aws_auth__hash_sha256(pool, canon_request.canon_request);

	// get string to sign
	const ngx_str_t *string_to_sign = ngx_aws_auth__string_to_sign(pool, key_scope, date, canon_request_hash);

	// generate signature
	const ngx_str_t *signature = ngx_aws_auth__sign_sha256_hex(pool, string_to_sign, signing_key);

	retval.signature = signature;
	retval.signed_header_names = canon_request.signed_header_names;
	retval.header_list = canon_request.header_list;
	return retval;
}


// list of header_pair_t
static inline const ngx_array_t* ngx_aws_auth__sign(ngx_pool_t *pool, ngx_http_request_t *req,
		const ngx_str_t *access_key_id,
		const ngx_str_t *signing_key,
		const ngx_str_t *key_scope,
		const ngx_str_t *s3_bucket_name,
    	const ngx_str_t *s3_endpoint,
		const ngx_str_t *security_token) {
	const struct AwsSignedRequestDetails signature_details =
		ngx_aws_auth__compute_signature(pool, req, signing_key, key_scope, s3_bucket_name, s3_endpoint, security_token);


	const ngx_str_t *auth_header_value = ngx_aws_auth__make_auth_token(pool, signature_details.signature,
											signature_details.signed_header_names, access_key_id, key_scope);

	header_pair_t *header_ptr;
	header_ptr = ngx_array_push(signature_details.header_list);
	header_ptr->key = AUTHZ_HEADER;
	header_ptr->value = *auth_header_value;

	return signature_details.header_list;
}

#endif