aws/request.scm

   1 ;;; guile-aws --- Scheme DSL for the AWS APIs
   2 ;;; Copyright © 2019 Ricardo Wurmus <rekado@elephly.net>
   3 ;;;
   4 ;;; Guile-AWS is free software: you can redistribute it and/or modify
   5 ;;; it under the terms of the GNU General Public License as published
   6 ;;; by the Free Software Foundation, either version 3 of the License,
   7 ;;; or (at your option) any later version.
   8 ;;;
   9 ;;; Guile-AWS is distributed in the hope that it will be useful, but
  10 ;;; WITHOUT ANY WARRANTY; without even the implied warranty of
  11 ;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12 ;;; General Public License for more details.
  13 ;;;
  14 ;;; You should have received a copy of the GNU General Public License
  15 ;;; along with this program.  If not, see
  16 ;;; <http://www.gnu.org/licenses/>.
  17
  18 (define-module (aws request)
  19   #:use-module (aws base)
  20   #:use-module (ice-9 match)
  21   #:use-module (ice-9 format)
  22   #:use-module (srfi srfi-1)
  23   #:use-module (srfi srfi-19)
  24   #:use-module (srfi srfi-26)
  25   #:use-module (gcrypt hash)
  26   #:use-module (gcrypt hmac)
  27   #:use-module (rnrs bytevectors)
  28   #:use-module (web client)
  29   #:use-module ((web http) #:select (header-writer))
  30   #:use-module (sxml simple)
  31   #:export (make-operation->request serialize-aws-value))
  32
  33 ;;; Commentary:
  34
  35 ;;; See: http://docs.aws.amazon.com/general/latest/gr/sigv4_signing.html
  36 ;;; Make a POST request and pass request parameters in the body of the
  37 ;;; request.  Auth information is provided in an Authorization header.
  38
  39 ;;; Code:
  40
  41 (define algorithm "AWS4-HMAC-SHA256")
  42
  43 (define (sign key msg)
  44   "Sign the string MSG with the secret key KEY (a bytevector) using the SHA256 algorithm."
  45   (sign-data key (string->utf8 msg) #:algorithm 'sha256))
  46
  47 (define (hexify bv)
  48   (format #f "~{~2,'0x~}" (bytevector->u8-list bv)))
  49
  50 \f
  51 ;; See https://docs.aws.amazon.com/AWSEC2/latest/APIReference/Query-Requests.html
  52 (define* (serialize-aws-value thing #:key (path '()) n (depth 0))
  53   (define top? (zero? depth))
  54   (cond
  55    ((aws-structure? thing)
  56     (filter-map (lambda (member)
  57                   (match (aws-member-value member)
  58                     ('__unspecified__ #f)
  59                     (value
  60                      (serialize-aws-value value
  61                                           #:path
  62                                           (if top?
  63                                               (list (or (aws-member-location-name member)
  64                                                         (aws-member-name member)))
  65                                               (cons* (or (aws-member-location-name member)
  66                                                          (aws-member-name member))
  67                                                      n
  68                                                      (aws-structure-aws-name thing)
  69                                                      path))
  70                                           #:depth
  71                                           (1+ depth)))))
  72                 (aws-structure-members thing)))
  73    ((aws-shape? thing)
  74     (cond
  75      ((aws-shape-primitive? thing)
  76       (serialize-aws-value (aws-shape-value thing)
  77                            #:path path
  78                            #:depth (1+ depth)))
  79      (else
  80       (serialize-aws-value (aws-shape-value thing)
  81                            #:path
  82                            (cons (or (aws-shape-location-name thing)
  83                                      (aws-shape-aws-name thing)) path)
  84                            #:depth (1+ depth)))))
  85    ((boolean? thing)
  86     (serialize-aws-value (or (and thing "true") "false")
  87                          #:path path
  88                          #:depth (1+ depth)))
  89    ((list? thing)
  90     (append-map (lambda (item n)
  91                   (serialize-aws-value item
  92                                        #:path path
  93                                        #:n n
  94                                        #:depth (1+ depth)))
  95                 thing
  96                 (iota (length thing) 1)))
  97    (else (format #f "~a=~a"
  98                  (string-join (map (cut format #f "~a" <>)
  99                                    (reverse (filter identity path)))
 100                               ".")
 101                  thing))))
 102
 103 (define* (make-operation->request api-metadata)
 104   "Return a procedure that accepts an operation and returns an HTTP request."
 105   (define endpoint-prefix
 106     (assoc-ref api-metadata 'endpointPrefix))
 107   (define service-name endpoint-prefix)
 108   (define api-version
 109     (assoc-ref api-metadata 'apiVersion))
 110
 111   (lambda* (#:key http operation-name input)
 112     (define region
 113       (or (getenv "AWS_DEFAULT_REGION")
 114           "us-west-2"))
 115     (define access-key
 116       (or (getenv "AWS_ACCESS_KEY_ID")
 117           (error "No access key available.  Set the AWS_ACCESS_KEY_ID environment variable.")))
 118     (define secret-key
 119       (or (getenv "AWS_SECRET_ACCESS_KEY")
 120           (error "No secret access key available.  Set the AWS_SECRET_ACCESS_KEY environment variable.")))
 121     (define method
 122       (assoc-ref http "method"))
 123     (define host
 124       (string-join (list endpoint-prefix
 125                          region
 126                          "amazonaws.com")
 127                    "."))
 128     (define endpoint
 129       (string-append "https://" host "/"))
 130     (define content-type
 131       '(application/x-www-form-urlencoded (charset . "utf-8")))
 132
 133     ;; DynamoDB needs this, others don't.
 134     (define amz-target (and=> (assoc-ref api-metadata 'targetPrefix)
 135                               (cut string-append <> "."
 136                                    operation-name)))
 137
 138     ;; TODO: some APIs use JSON, others (like EC2) use plain query strings.
 139     (define request-parameters
 140       (string-join (cons* (format #f "Action=~a" operation-name)
 141                           (format #f "Version=~a" api-version)
 142                           (serialize-aws-value input))
 143                    "&"))
 144
 145     (define now (current-date 0))
 146     (define amz-date
 147       (date->string now "~Y~m~dT~H~M~SZ"))
 148     (define date-stamp
 149       (date->string now "~Y~m~d"))
 150
 151     \f
 152     ;; https://docs.aws.amazon.com/general/latest/gr/sigv4-create-canonical-request.html
 153
 154     ;; TODO: Create canonical URI--the part of the URI from domain to query
 155     ;; string (use '/' if no path)
 156     (define canonical-uri "/")
 157
 158     (define headers
 159       (filter cdr `((content-type . ,content-type)
 160                     (host         . (,host . #f))
 161                     (x-amz-date   . ,amz-date)
 162                     (x-amz-target . ,amz-target))))
 163     (define authorization-header
 164       (let* ((canonical-headers
 165               ;; Header names must be trimmed, lower-case, sorted in
 166               ;; code point order from low to high!  Note: there must
 167               ;; be a trailing newline character.
 168               (string-join (map (match-lambda
 169                                   ((key . value)
 170                                    (string-append (symbol->string key) ":"
 171                                                   (with-output-to-string
 172                                                     (lambda ()
 173                                                       ((header-writer key) value (current-output-port)))))))
 174                                 headers)
 175                            "\n" 'suffix))
 176              (signed-headers
 177               ;; This lists the headers in the canonical-headers list,
 178               ;; delimited with ";" and in alpha order.  The request
 179               ;; can include any headers; canonical-headers and
 180               ;; signed-headers include those that you want to be
 181               ;; included in the hash of the request. "Host" and
 182               ;; "x-amz-date" are always required.
 183               (string-join (map (compose symbol->string first) headers) ";"))
 184              ;; The query string is blank because parameters are passed
 185              ;; in the body of the request.
 186              (canonical-querystring "")
 187              (canonical-request
 188               (string-join (list method
 189                                  canonical-uri
 190                                  canonical-querystring
 191                                  canonical-headers
 192                                  signed-headers
 193                                  ;; The payload hash
 194                                  (hexify (sha256 (string->utf8 request-parameters))))
 195                            "\n"))
 196              (credential-scope
 197               (string-join (list date-stamp
 198                                  region
 199                                  service-name
 200                                  "aws4_request") "/"))
 201              (string-to-sign
 202               (string-join (list algorithm
 203                                  amz-date
 204                                  credential-scope
 205                                  (hexify (sha256 (string->utf8 canonical-request))))
 206                            "\n"))
 207              (signature
 208               (let* ((kdate       (sign (string->utf8 (string-append "AWS4" secret-key)) date-stamp))
 209                      (kregion     (sign kdate region))
 210                      (kservice    (sign kregion service-name))
 211                      (signing-key (sign kservice "aws4_request")))
 212                 (hexify (sign signing-key string-to-sign)))))
 213         `(,(string->symbol algorithm)
 214           (Credential . ,(string-append access-key "/" credential-scope))
 215           (SignedHeaders . ,signed-headers)
 216           (Signature . ,signature))))
 217
 218     ;; For DynamoDB, the request can include any headers, but MUST
 219     ;; include "host", "x-amz-date", "x-amz-target", "content-type",
 220     ;; and "Authorization".  Except for the authorization header, the
 221     ;; headers must be included in the canonical-headers and
 222     ;; signed-headers values, as noted earlier.  Order here is not
 223     ;; significant.
 224     (define new-headers
 225       (cons `(Authorization . ,authorization-header)
 226             (filter cdr headers)))
 227
 228     (call-with-values
 229         (lambda ()
 230           (http-post endpoint
 231                      ;#:method (string->symbol method)
 232                         #:body (string->utf8 request-parameters)
 233                         #:headers new-headers))
 234       (lambda (response body)
 235         (xml->sxml (match body
 236                      ((? bytevector? bv)
 237                       (utf8->string bv))
 238                      ((? string? s) s)))))))