API调用问题答案

【问题标题】：Issue with API callAPI调用问题
【发布时间】：2018-09-28 10:30:03
【问题描述】：

我正在尝试使用以下方法将一些数据点发送到 Web api。（不确定是否共享密钥，所以我省略了一部分）。

library(jsonlite)
library(httr)

url = "https://api.marketcycles.online/api/CycleScanner"
t <- 1:101
val <- 2*sin(2*pi*t/25) + 5*cos(2*pi*t/50)
val[1:3]
body.list <- list(datapoints = val)
query.list <- list(api_Key = "wtt****")
res <- POST(url = url, query = query.list, body = body.list,
            encode = "json")
a <- content(res, as = "text")
b <- fromJSON(a)
b[[2]]

这会导致错误“对象引用未设置为对象的实例”

以下 curl 命令有效（我已经删除了大部分数据点）

curl -X POST --header 'Content-Type: application/json' \
    --header 'Accept: application/json' \
    -d '[5.458,5.8064,6.018,....5,5.458]' \
    'https://api.marketcycles.online/api/CycleScanner?api_Key=wtt****'

关于使 POST 命令正常工作的任何建议？

感谢 hrbrmstr 的回答。非常感激。我尝试了以下

httr::POST(
  url = "https://api.marketcycles.online/api/CycleScanner",
  httr::content_type_json(),
  httr::accept_json(),
  encode = "json", 
  body = jsonlite::toJSON(val),
  query = list(
    amplitudeMulti = "1.0",
    bartelsLimit = "49",
    minCycleLength = "5",
    maxCycleLength = "300",
    sortByStrength = "true",
    includeSpectrum = "false",
    humanReadableText = "false",
    api_Key = "wtt****")
)

无论有无 content_type_jason() 行，在两种情况下都收到以下错误

b[[1]]
[1] "The request contains an entity body but no Content-Type header. The
inferred media type 'application/octet-stream' is not supported for this
resource."
b[[2]]
[1] "No MediaTypeFormatter is available to read an object of type
'Double[]' from content with media type 'application/octet-stream'."
b[[3]]
[1] "System.Net.Http.UnsupportedMediaTypeException"

据我了解，当正文是列表时， encode() 提供列表元素的格式。我不清楚当它不是时该怎么做。我查看了 httr 源代码，有一个未记录的函数 body_config，但不确定在 POST 命令中使用它。有什么解决这个问题的建议吗？

【问题讨论】：

标签： r post httr

【解决方案1】：

我没有 API 密钥（你 100% 正确不分享你的），但他们的 Swagger API Docs 有点谎言他们的期望作为输入。

我在他们提供的在线 Swagger 测试器中使用了带有该端点的假 API 密钥（知道它会失败但仍然显示 curl 行）并填充默认值以全面了解端点的期望和它还给了这个（格式是我的，一整行回来了）：

curl 
  -X POST 
  --header 'Content-Type: application/json' 
  --header 'Accept: application/json' 
  -d '[5.458,5.8064,6.018,6.0702,5.9472,5.6409,5.1517,4.4888,3.6699,2.7207,1.6732,0.5646,-0.5646,-1.6732,-2.7207,-3.6699,-4.4888,-5.1517,-5.6409,-5.9472,-6.0702,-6.018,-5.8064,-5.458,-5,-4.4632,-3.8794,-3.2798,-2.6929,-2.143,-1.6488,-1.2225,-0.8695,-0.5879,-0.3695,-0.2007,-0.0633,0.0633,0.2007,0.3695,0.5879,0.8695,1.2225,1.6488,2.143,2.6929,3.2798,3.8794,4.4632,5,5.458,5.8064,6.018,6.0702,5.9472,5.6409,5.1517,4.4888,3.6699,2.7207,1.6732,0.5646,-0.5646,-1.6732,-2.7207,-3.6699,-4.4888,-5.1517,-5.6409,-5.9472,-6.0702,-6.018,-5.8064,-5.458,-5,-4.4632,-3.8794,-3.2798,-2.6929,-2.143,-1.6488,-1.2225,-0.8695,-0.5879,-0.3695,-0.2007,-0.0633,0.0633,0.2007,0.3695,0.5879,0.8695,1.2225,1.6488,2.143,2.6929,3.2798,3.8794,4.4632,5,5.458]' 
  'https://api.marketcycles.online/api/CycleScanner?amplitudeMulti=1.0&bartelsLimit=49&minCycleLength=5&maxCycleLength=300&sortByStrength=true&includeSpectrum=false&humanReadableText=false&api_Key=aaaa'

这表明文档在暗示 datapoints 值被命名时是在撒谎。它不是。这可能是导致您的错误的原因。

我通过curlconverter 运行原始的、生成的curl 命令行，并将其作为httr 模板提供：

httr::VERB(
  verb = "POST", 
  url = "https://api.marketcycles.online/api/CycleScanner",
  httr::add_headers(Accept = "application/json"),
  body = "[5.458,5.8064,6.018,6.0702,5.9472,5.6409,5.1517,4.4888,3.6699,2.7207,1.6732,0.5646,-0.5646,-1.6732,-2.7207,-3.6699,-4.4888,-5.1517,-5.6409,-5.9472,-6.0702,-6.018,-5.8064,-5.458,-5,-4.4632,-3.8794,-3.2798,-2.6929,-2.143,-1.6488,-1.2225,-0.8695,-0.5879,-0.3695,-0.2007,-0.0633,0.0633,0.2007,0.3695,0.5879,0.8695,1.2225,1.6488,2.143,2.6929,3.2798,3.8794,4.4632,5,5.458,5.8064,6.018,6.0702,5.9472,5.6409,5.1517,4.4888,3.6699,2.7207,1.6732,0.5646,-0.5646,-1.6732,-2.7207,-3.6699,-4.4888,-5.1517,-5.6409,-5.9472,-6.0702,-6.018,-5.8064,-5.458,-5,-4.4632,-3.8794,-3.2798,-2.6929,-2.143,-1.6488,-1.2225,-0.8695,-0.5879,-0.3695,-0.2007,-0.0633,0.0633,0.2007,0.3695,0.5879,0.8695,1.2225,1.6488,2.143,2.6929,3.2798,3.8794,4.4632,5,5.458]",
  encode = "json", 
  query = list(
    amplitudeMulti = "1.0",
    bartelsLimit = "49",
    minCycleLength = "5",
    maxCycleLength = "300",
    sortByStrength = "true",
    includeSpectrum = "false",
    humanReadableText = "false",
    api_Key = "aaaa"
  )
)

它比所需的 b/c 更详细，它是以编程方式生成的。要将其放入您的原始代码中：

httr::POST(
  url = "https://api.marketcycles.online/api/CycleScanner",
  httr::accept_json()
  encode = "json", 
  body = jsonlite::toJSON(val),
  query = list(
    amplitudeMulti = "1.0",
    bartelsLimit = "49",
    minCycleLength = "5",
    maxCycleLength = "300",
    sortByStrength = "true",
    includeSpectrum = "false",
    humanReadableText = "false",
    api_Key = "aaaa"
  )
)

可能有效。同样，我只是通过 Swagger 去测试它。您也可以删除 query 位中的所有默认值。我喜欢在构建与 API 接口的包时传递它们。

【讨论】：

感谢您的 cmets。我喜欢卷曲转换器的想法。

【解决方案2】：

找到了解决办法。这是对 hrbrmstr 建议的代码的一些调整。以下代码有效

httr::POST(
  url = "https://api.marketcycles.online/api/CycleScanner",
  httr::content_type_json(), # needed to add this
  httr::accept_json(),
  body =jsonlite::toJSON(val),
  # encode = "json", # needed to delete this 
  query = list(
    amplitudeMulti = "1.0",
    bartelsLimit = "49",
    minCycleLength = "5",
    maxCycleLength = "300",
    sortByStrength = "true",
    includeSpectrum = "false",
    humanReadableText = "false",
    api_Key = "wtt****")
)

感谢您的帮助。

【讨论】：