(Tcl) curl with Variable Substitution in a GraphQL Request Body

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This example shows how to use variables inside a graphql request body using the {{variable_name}} syntax. When the HTTP request’s Content-Type indicates graphql, Chilkat automatically applies proper escaping to each substituted value, ensuring the resulting graphql remains valid.

Note: This example requires Chilkat v11.5.0 or greater.

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load ./chilkat.dll

set success 0

set success 0

# Variable names are enclosed between {{ and }}
# Important: Variables should be placed inside the quotes.

# curl -X POST https://api.example.com/graphql \
#   -H "Content-Type: application/graphql; charset=utf-8" \
#   -H "Accept: application/json" \
#   --data-binary "mutation {
#   createUser(
#     input: {
#       name: \"{{name}}\"
#       city: \"{{city}}\"
#       note: \"{{note}}\"
#       bio: \"{{bio}}\"
#     }
#   ) {
#     id
#     name
#   }
# }"

# Build the above curl command.
set sbCurl [new_CkStringBuilder]

CkStringBuilder_AppendLn $sbCurl "curl -X POST https://api.example.com/graphql \\"
CkStringBuilder_AppendLn $sbCurl "  -H \"Content-Type: application/graphql; charset=utf-8\" \\"
CkStringBuilder_AppendLn $sbCurl "  -H \"Accept: application/json\" \\"
CkStringBuilder_AppendLn $sbCurl "  -d \"mutation {"
CkStringBuilder_AppendLn $sbCurl "  createUser("
CkStringBuilder_AppendLn $sbCurl "    input: {"
CkStringBuilder_AppendLn $sbCurl "      name: \\\"{{name}}\\\""
CkStringBuilder_AppendLn $sbCurl "      city: \\\"{{city}}\\\""
CkStringBuilder_AppendLn $sbCurl "      note: \\\"{{note}}\\\""
CkStringBuilder_AppendLn $sbCurl "      bio: \\\"{{bio}}\\\""
CkStringBuilder_AppendLn $sbCurl "    }"
CkStringBuilder_AppendLn $sbCurl "  ) {"
CkStringBuilder_AppendLn $sbCurl "    id"
CkStringBuilder_AppendLn $sbCurl "    name"
CkStringBuilder_AppendLn $sbCurl "  }"
CkStringBuilder_AppendLn $sbCurl "}\""

set curl [new_CkHttpCurl]

# Provide values for variables
CkHttpCurl_SetVar $curl "name" "José O'Connor"
CkHttpCurl_SetVar $curl "city" "München"
CkHttpCurl_SetVar $curl "note" "He said \"Hello, world!\" — and left…"
CkHttpCurl_SetVar $curl "bio" "Loves sushi, café visits, and π ≈ 3.14159"

# To demonstrate how the variables are replaced, this example does not execute the curl command. 
# Instead, it generates the raw HTTP request that would be sent if the curl command were run.
set sbRawRequest [new_CkStringBuilder]

set success [CkHttpCurl_ToRawRequest $curl [CkStringBuilder_getAsString $sbCurl] $sbRawRequest]
if {$success == 0} then {
    puts [CkHttpCurl_lastErrorText $curl]
    delete_CkStringBuilder $sbCurl
    delete_CkHttpCurl $curl
    delete_CkStringBuilder $sbRawRequest
    exit
}

puts [CkStringBuilder_getAsString $sbRawRequest]

# The output is shown below.
# Notice the quote chars around "Hello, world!" are properly escaped.

# POST /graphql HTTP/1.1
# Accept: application/json
# Host: api.example.com
# Content-Type: application/graphql; charset=utf-8
# Content-Length: 250
# 
# mutation {
#   createUser(
#     input: {
#       name: "José O'Connor"
#       city: "München"
#       note: "He said \"Hello, world!\" — and left…"
#       bio: "Loves sushi, café visits, and π ≈ 3.14159"
#     }
#   ) {
#     id
#     name
#   }
# }

delete_CkStringBuilder $sbCurl
delete_CkHttpCurl $curl
delete_CkStringBuilder $sbRawRequest