Msearch Elasticsearch API - Rust - elasticsearch

Question

By this point, I feel like I am the only other person on earth that is using multi-search on Rust... other than the person who wrote it.
There is zero documentation on this other than this hyper-confusing one https://docs.rs/elasticsearch/7.14.0-alpha.1/elasticsearch/struct.Msearch.html
I figured I had to pass MsearchParts parts as an argument for the client.msearch(here goes msearch_parts), and luckily for me, there a piece of documentation for how that is supposed to be, but such documentation is so poorly done that I have no clue of what to do because I did not write the API.
I have no clue of how to pass my JSON
{"index":"cat_food"}
{"query":{"term":{"name":{"term":"Whiskers"}}}}
{"index":"cat_food"}
{"query":{"term":{"name":{"term":"Chicken"}}}}
{"index":"cat_food"}
{"query":{"term":{"name":{"term":"Turkey"}}}}
"NOT IN THE CODE: extra EMPTY line required by elasticsearch multi-searches"
and get a 200^ response.
As a side note, my JSON is well formatted into a string that can be sent in a normal reqwest the issue is more on how to turn that JSON string into MsearchParts.

Answer 1

The body needs to conform to the structure specified for the msearch API
The multi search API executes several searches from a single API
request. The format of the request is similar to the bulk API format
and makes use of the newline delimited JSON (NDJSON) format.
The structure is as follows:
header\n
body\n
header\n
body\n
let client = Elasticsearch::default();
let msearch_response = client
.msearch(MsearchParts::None)
.body::<JsonBody<Value>>(vec![
json!({"index":"cat_food"}).into(),
json!({"query":{"term":{"name":{"term":"Whiskers"}}}}).into(),
json!({"index":"cat_food"}).into(),
json!({"query":{"term":{"name":{"term":"Chicken"}}}}).into(),
json!({"index":"cat_food"}).into(),
json!({"query":{"term":{"name":{"term":"Turkey"}}}}).into(),
])
.send()
.await?;
let json: Value = msearch_response.json().await?;
// enumerate over the response objects in the response
for (idx, response) in json["responses"]
.as_array()
.unwrap()
.into_iter()
.enumerate()
{
println!();
println!("response {}", idx);
println!();
// print the name of each matching document
for hit in response["hits"]["hits"].as_array().unwrap() {
println!("{}", hit["_source"]["name"]);
}
}
The above example uses MsearchParts::None, but because all search requests are targeting the same index, the index can be specified with MsearchParts::Index(...), and it doesn't need to be repeated in the header for each search request
let client = Elasticsearch::default();
let msearch_response = client
.msearch(MsearchParts::Index(&["cat_food"]))
.body::<JsonBody<Value>>(vec![
json!({}).into(),
json!({"query":{"term":{"name":{"term":"Whiskers"}}}}).into(),
json!({}).into(),
json!({"query":{"term":{"name":{"term":"Chicken"}}}}).into(),
json!({}).into(),
json!({"query":{"term":{"name":{"term":"Turkey"}}}}).into(),
])
.send()
.await?;
let json: Value = msearch_response.json().await?;
// enumerate over the response objects in the response
for (idx, response) in json["responses"]
.as_array()
.unwrap()
.into_iter()
.enumerate()
{
println!();
println!("response {}", idx);
println!();
// print the name of each matching document
for hit in response["hits"]["hits"].as_array().unwrap() {
println!("{}", hit["_source"]["name"]);
}
}
Because msearch's body() fn takes a Vec<T> where T implements the Body trait, and Body is implemented for &str, you can pass a string literal directly
let msearch_response = client
.msearch(MsearchParts::None)
.body(vec![r#"{"index":"cat_food"}
{"query":{"term":{"name":{"term":"Whiskers"}}}}
{"index":"cat_food"}
{"query":{"term":{"name":{"term":"Chicken"}}}}
{"index":"cat_food"}
{"query":{"term":{"name":{"term":"Turkey"}}}}
"#])
.send()
.await?;
let json: Value = msearch_response.json().await?;

Answer 2

Per the doc of MsearchParts, it looks an array of &str needs to be used to construct the Index (or IndexType) variant of enum MsearchParts. So, please give the following way a try and see if it works.
Let parts = MsearchParts::Index([
r#"{"index":"cat_food"}"#,
r#"{"query":{"term":{"name":{"term":"Whiskers"}}}}"#,
r#"{"index":"cat_food"}"#,
r#"{"query":{"term":{"name":{"term":"Chicken"}}}}"#,
r#"{"index":"cat_food"}"#,
r#"{"query":{"term":{"name":{"term":"Turkey"}}}}"#
]);

Answer 3

After hours of investigating I took some other approach, using a body vector and the msearch API.
I think the json doesnt go to the msearchparts but to a vector of bodies.
(see https://docs.rs/elasticsearch/7.14.0-alpha.1/elasticsearch/#request-bodies)
It runs, but the response gives me an error 400. And I dont know why.
I assume its the missing empty (json) bodies, as required in the elastic console.
What do you think?
let mut body: Vec<JsonBody<_>> = Vec::with_capacity(4);
body.push(json!(
{"query": {
"match": {"title":"bee"}
}}
).into());
body.push(json!(
{"query": {
"multi_match": {
"query": "tree",
"fields": ["title", "info"]
}
},"from":0, "size":2}
).into());
let search_response = client
.msearch(MsearchParts::Index(&["nature_index"]))
.body(body)
.send()
.await?;