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;;; guile-aws --- Scheme DSL for the AWS APIs
;;; Copyright © 2019 Ricardo Wurmus <rekado@elephly.net>
;;;
;;; Guile-AWS is free software: you can redistribute it and/or modify
;;; it under the terms of the GNU General Public License as published
;;; by the Free Software Foundation, either version 3 of the License,
;;; or (at your option) any later version.
;;;
;;; Guile-AWS is distributed in the hope that it will be useful, but
;;; WITHOUT ANY WARRANTY; without even the implied warranty of
;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
;;; General Public License for more details.
;;;
;;; You should have received a copy of the GNU General Public License
;;; along with this program. If not, see
;;; <http://www.gnu.org/licenses/>.
(define-module (aws request)
#:use-module (aws base)
#:use-module (ice-9 match)
#:use-module (ice-9 format)
#:use-module (srfi srfi-1)
#:use-module (srfi srfi-19)
#:use-module (srfi srfi-26)
#:use-module (gcrypt hash)
#:use-module (gcrypt hmac)
#:use-module (rnrs bytevectors)
#:use-module (web client)
#:use-module ((web http) #:select (header-writer))
#:use-module (sxml simple)
#:export (make-operation->request serialize-aws-value))
;;; Commentary:
;;; See: http://docs.aws.amazon.com/general/latest/gr/sigv4_signing.html
;;; Make a POST request and pass request parameters in the body of the
;;; request. Auth information is provided in an Authorization header.
;;; Code:
(define algorithm "AWS4-HMAC-SHA256")
(define (sign key msg)
"Sign the string MSG with the secret key KEY (a bytevector) using the SHA256 algorithm."
(sign-data key (string->utf8 msg) #:algorithm 'sha256))
(define (hexify bv)
(format #f "~{~2,'0x~}" (bytevector->u8-list bv)))
;; See https://docs.aws.amazon.com/AWSEC2/latest/APIReference/Query-Requests.html
(define* (serialize-aws-value thing #:key (path '()) n (depth 0))
(define top? (zero? depth))
(cond
((aws-structure? thing)
(filter-map (lambda (member)
(match (aws-member-value member)
('__unspecified__ #f)
(value
(serialize-aws-value value
#:path
(if top?
(list (or (aws-member-location-name member)
(aws-member-name member)))
(cons* (or (aws-member-location-name member)
(aws-member-name member))
n
(aws-structure-aws-name thing)
path))
#:depth
(1+ depth)))))
(aws-structure-members thing)))
((aws-shape? thing)
(cond
((aws-shape-primitive? thing)
(serialize-aws-value (aws-shape-value thing)
#:path path
#:depth (1+ depth)))
(else
(serialize-aws-value (aws-shape-value thing)
#:path
(cons (or (aws-shape-location-name thing)
(aws-shape-aws-name thing)) path)
#:depth (1+ depth)))))
((boolean? thing)
(serialize-aws-value (or (and thing "true") "false")
#:path path
#:depth (1+ depth)))
((list? thing)
(append-map (lambda (item n)
(serialize-aws-value item
#:path path
#:n n
#:depth (1+ depth)))
thing
(iota (length thing) 1)))
(else (format #f "~a=~a"
(string-join (map (cut format #f "~a" <>)
(reverse (filter identity path)))
".")
thing))))
(define* (make-operation->request api-metadata)
"Return a procedure that accepts an operation and returns an HTTP request."
(define endpoint-prefix
(assoc-ref api-metadata 'endpointPrefix))
(define service-name endpoint-prefix)
(define api-version
(assoc-ref api-metadata 'apiVersion))
(lambda* (#:key http operation-name input)
(define region
(or (getenv "AWS_DEFAULT_REGION")
"us-west-2"))
(define access-key
(or (getenv "AWS_ACCESS_KEY_ID")
(error "No access key available. Set the AWS_ACCESS_KEY_ID environment variable.")))
(define secret-key
(or (getenv "AWS_SECRET_ACCESS_KEY")
(error "No secret access key available. Set the AWS_SECRET_ACCESS_KEY environment variable.")))
(define method
(assoc-ref http "method"))
(define host
(string-join (list endpoint-prefix
region
"amazonaws.com")
"."))
(define endpoint
(string-append "https://" host "/"))
(define content-type
'(application/x-www-form-urlencoded (charset . "utf-8")))
;; DynamoDB needs this, others don't.
(define amz-target (and=> (assoc-ref api-metadata 'targetPrefix)
(cut string-append <> "."
operation-name)))
;; TODO: some APIs use JSON, others (like EC2) use plain query strings.
(define request-parameters
(string-join (cons* (format #f "Action=~a" operation-name)
(format #f "Version=~a" api-version)
(serialize-aws-value input))
"&"))
(define now (current-date 0))
(define amz-date
(date->string now "~Y~m~dT~H~M~SZ"))
(define date-stamp
(date->string now "~Y~m~d"))
;; https://docs.aws.amazon.com/general/latest/gr/sigv4-create-canonical-request.html
;; TODO: Create canonical URI--the part of the URI from domain to query
;; string (use '/' if no path)
(define canonical-uri "/")
(define headers
(filter cdr `((content-type . ,content-type)
(host . (,host . #f))
(x-amz-date . ,amz-date)
(x-amz-target . ,amz-target))))
(define authorization-header
(let* ((canonical-headers
;; Header names must be trimmed, lower-case, sorted in
;; code point order from low to high! Note: there must
;; be a trailing newline character.
(string-join (map (match-lambda
((key . value)
(string-append (symbol->string key) ":"
(with-output-to-string
(lambda ()
((header-writer key) value (current-output-port)))))))
headers)
"\n" 'suffix))
(signed-headers
;; This lists the headers in the canonical-headers list,
;; delimited with ";" and in alpha order. The request
;; can include any headers; canonical-headers and
;; signed-headers include those that you want to be
;; included in the hash of the request. "Host" and
;; "x-amz-date" are always required.
(string-join (map (compose symbol->string first) headers) ";"))
;; The query string is blank because parameters are passed
;; in the body of the request.
(canonical-querystring "")
(canonical-request
(string-join (list method
canonical-uri
canonical-querystring
canonical-headers
signed-headers
;; The payload hash
(hexify (sha256 (string->utf8 request-parameters))))
"\n"))
(credential-scope
(string-join (list date-stamp
region
service-name
"aws4_request") "/"))
(string-to-sign
(string-join (list algorithm
amz-date
credential-scope
(hexify (sha256 (string->utf8 canonical-request))))
"\n"))
(signature
(let* ((kdate (sign (string->utf8 (string-append "AWS4" secret-key)) date-stamp))
(kregion (sign kdate region))
(kservice (sign kregion service-name))
(signing-key (sign kservice "aws4_request")))
(hexify (sign signing-key string-to-sign)))))
`(,(string->symbol algorithm)
(Credential . ,(string-append access-key "/" credential-scope))
(SignedHeaders . ,signed-headers)
(Signature . ,signature))))
;; For DynamoDB, the request can include any headers, but MUST
;; include "host", "x-amz-date", "x-amz-target", "content-type",
;; and "Authorization". Except for the authorization header, the
;; headers must be included in the canonical-headers and
;; signed-headers values, as noted earlier. Order here is not
;; significant.
(define new-headers
(cons `(Authorization . ,authorization-header)
(filter cdr headers)))
(call-with-values
(lambda ()
(http-post endpoint
;#:method (string->symbol method)
#:body (string->utf8 request-parameters)
#:headers new-headers))
(lambda (response body)
(xml->sxml (match body
((? bytevector? bv)
(utf8->string bv))
((? string? s) s)))))))
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